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PRACTICAL 

Dental Metallurgy 



A TEXT- AND REFERENCE-BOOK 

FOR 

STUDENTS AND PRACTITIONERS OF DENTISTRY 



Embodying the Principles of Metallurgy, and their Applica- 
tion to Dentistry, including an Addendum of 
Collateral Literature, and 
Experiments. 



BY 

JOSEPH DUPUY ^HODGEN, D. D. S. 

Assistant to the Chair of ^Dental Chemistry and Metallurgy, 

College of ^Dentistry, University of California; 

Late Editor of Pacific Coast 'Dentist. 



SECOND EDITION 

COMPLETELY REVISED, REARRANGED, AND ENLARGED. 



SAN FRANCISCO : 

THE HTCKS-JUDI) CO, 

PRINTERS, PUBLISHERS, AND BOOKBINDERS'! 

1897. 




TWO COPIES RECEIVED 






Entered according to Act of Congress, in the year 1897, 

By Joseph D. Hodgen, 

In the office of the Librarian of Congress, at Washington, D. C. 



TO 

CLARK LA MOTTE GODDARD, A. M., D. D. S., 

Professor of Orthodontia, 
College of Dentistry, University of California, 

THIS WORK IS INSCRIBED, 

IN 

ADMIRATION OF HIS TALENTS, 

AND 

GRATITUDE FOR HIS TEACHINGS, CRITICISMS, 
AND FRIENDSHIP. 



PREFACE TO FIRST EDITION. 



In presenting this little volume to the practitioner and 
student of the dental profession, the author does not natter 
himself that he is filling a void in such literature, or that a 
crying need has been felt in the profession for this particular 
production. It has, however, grown out of the exigencies of 
the writer's own classroom and laborator} 7 , after several years' 
practical experience as an instructor on its subject. 

The endeavor has not been to furnish a scientific and ex- 
haustive treatise on metallurgy, but rather to present, in a clear 
and practical manner, the principles of that subject as the 
author sees them related and applicable to the every-day wants 
of the dentist. 

Keenly appreciating the reluctance with which this and the 
analogous study of chemistry have been pursued by the aver- 
age student, the author has sought to awaken a deserving 
interest by doing away with the usual lectures, and employing 
the work as a text-book, subject to explanatory elaboration 
during the recitation; and to further make it so practical that 
it may be taken into the metallurgical laboratory and used as 
a manual for practical and experimental work. It presupposes 
the student to possess a fair knowledge of the principles of 
inorganic chemistry, comprehending the reading and writing of 
formulae, atomic affinities, and the expression of equations. 

An addendum refers the interested student to the opinions 
of others, and more elaborate essays, papers, and discussion by 
authors who have made a particular study of some principle 
merely hinted at in the text. In the selection of these, the 
object has been to refer to those most available to all students, 
and not to intimate that other publications are devoid of equally 
scientific and instructive productions. 

The author has freely consulted and quoted from whatever 
works on metallurgy and allied subjects were in his reach, 
especially the exceptionally scientific papers on amalgams by 
Prof. G. V. Black, published in the Dental Cosmos; and the val- 
uable contributions to the American System of Dentistry, entitled 
Dental Metallurgy, by Dr. Edward C. Kirk ; Brannt's Metallic 



Alloys; the works on metallurgy by Makins, Fletcher, Essig, 
Mitchell ; the chemistries of Roscoe, Bloxam, and many others, 
found in the library of the California Mining Eureau, through 
the kindness of the State Mineralogist, Mr. J. J. Crawford ; 
together with the Denial Cosmos, Denial Review, International 
Denial Journal, and several others. To the authors and editors 
of these, the author takes this opportunity to express his grate- 
fulness for the liberties taken. 

For valuable criticisms and suggestions the author is 
especially grateful to Prof. C. L. Goddard, and also wishes to 
express his obligation to the firm of J. H. A. Folkers & Bro. for 
courtesies so kindly extended; also to Dr. S. Eldred Gilbert, 
Hastings & Co., Hood & Reynolds, and a number of other 
Eastern manufacturers, for their prompt responses to inquiry. 

JOSEPH D. HODGEN. 



PREFACE TO SECOND EDITION. 



The kindly reception and success accorded the first edition 
of Practical Dental Metallurgy has made a second edition 
necessary to fill the wants of the numerous colleges which have 
adopted the work as a text for their classes in this branch of 
science. 

The present edition is completely revised, rearranged and 
somewhat enlarged. The chapters on amalgams have been 
placed after the discussion of the metals individually, with the 
belief that such an arrangement will facilitate a more compre- 
hensive grasp of this most important subject. These chapters 
have been wholly revised with a conscientious endeavor to present 
the newest facts and most accurate data attainable, thus keeping 
the book abreast with the scientific investigations of the day. 

The more than kind words which have come to me so fre- 
quently through the professional press, from fellow teachers, and 
the profession generally have been a source of much pleasure to 
me and I wish to express my gratitude for all the encouragement 
which has been so generously extended. 

JOSEPH D. HODGEN. 
No. 1005 Sutter Street, 

San Francisco, August 30, 1897. 



CONTENTS. 



Chapter Page 

I. Introduction 9 

II. The Properties of Metals 19 

III. Combination of Metals with Non-Metallic Elements. 35 

IV. Melting Metals 50 

V. Alloys 83 

VI. Lead 98 

VII. Antimony. .. 108 

VIII. Tin 114 

IX. Bismuth 125 

X. Zinc 134 

XI. Cadmium 148 

XII. Copper 153 

XIII. Iron 165 

XIV. Aluminum 185 

XV. Mercury 198 

XVI. Silver 211 

XVII. Iridium 229 

XVIII. Palladium 233 

XIX. Platinum 238 

XX. Gold 246 

XXI. Amalgams 293 

XXII. Classified Amalgams 318 

ADDENDUM— Collateral Literature 335 



PRACTICAL 
DENTAL METALLURGY. 



CHAPTER I. 
INTRODUCTION. 

CHEMISTRY is that branch of science which 
treats of the atomic conditions of matter, and espe- 
cially of atomic changes. It comprehends the combina- 
tion of diverse forms of matter producing new compounds, 
and the separating of already existing compounds into 
simpler ones, or resolving them into their ultimate princi- 
ples, which are called — 

ELEMENTS. — Substances whose molecules con- 
tain one kind of atoms only, and which all physical or 
chemical processes have as yet failed to break up or 
decompose into two or more dissimilar substances. It is 
not asserted that these substances are absolutely simple 
or elementary, or that they may not be found hereafter 
to yield more than one kind of matter, but merely so far 
as our knowledge extends it is so; indeed, recent spectro- 
scopic researches favor the impression that some, at 
least, of the elements are, perhaps, compounds of simple 
bodies. 

Sixty-six elements are at present known to us, of 
which the following is a list, arranged according to their 
electropositive and negative quality, or the electrochem- 
ical series. The most important are distinguished in the 
table by capitals, whilst those which at present are of 
slight importance, on account of their rare occurrence, or 
of our insufficient knowledge of their properties, are 
given in italics. 



10 



PRACTICAL DENTAL METALLURGY. 



TABLE OF ELEMENTS. 



NEGATIVE END. 



S3^mbol. 



o 

s 

N 

F 

CI 

Br 

I 

Se 

P 

As 

Cr 

V 

Mo 

W 

B 

C 

Sb 

Te 

Ta 

Cb 

Ti 

Si 

H 

Au 

OS 

Ir 

Pt 

Rh 

Ru 

Pd 

Hg 

Ag 

Cu 



Name. 



OXYGEN 

SULPHUR 

NITROGEN 

FLUORINE 

CHLORINE 

BROMINE 

IODINE 

Selenium 

PHOSPHORUS j 

ARSENICUM | 

CHROMIUM j 

Vanadium | 

Molybdenum 

Tungsten (Wolfram) j 

BORON I 

CARBON 

ANTIMONY (Stibium) . . . . 

Tellurium 

Tantalum 

Columbium (Niobium) 

Titanium '. 

SILICON 

HYDROGEN 

GOLD (Aurum) 

Osmium 

Iridium 

PLATINUM 

Rhodium 

Ruthenium 

Palladium 

MERCURY(Hydrargyrum) 

SILVER (Argeutum) 

COPPER (Cuprum) 



Valence. 



II 

II, IV, VI 
I, III, V. . 

I 



I, III, V, VII ... 
I, III, V, VII... 

I, III, V, VII. . . 

II, IV, VI 

III, V 

Ill, V 

II, (Cu 2 ) V[ , VI.. 

III, V 

II, IV, VI 

II, IV, VI 

Ill 

II, IV 

III, V 

II, IV, VI 

Ill V 

III, V 

IV 

IV 

I 

I, III 

II, IV, VI, VIII 

II, IV 

II, IV 

II, IV 

II, IV, VI. VIII 

II, IV 

II, (Hg 2 ) ir 

I 

II, (Cu a ) TI 



Atomic 
Weight. 



15.96 

31.98 

14.02 

18.98 

35.37 

79.76 

126.55 

78.79 

30.95 

74.91 

52.00 

51.25 

95.52 

183.61 

10.94 

11.97 

119.95 

127.96 

182.14 

93.81 

47.99 

28.19 

l.OO 

196.15 

198.49 

192.65 

194.41 

104.05 

104.21 

105.73 

199.71 

107.67 

63.17 



INTRODUCTION. 



11 



TABLE,' OF ELEMENTS— Continued. 



NEGATIVE] END. 



Symbol. 



Valence. 



u 

Bi 

Sa 

In 

Pb 

Cd 

Tl 

Co 

Ni 

Fe 

Zn 

Ga 

Mn 

La 

D 

Ce 

Th 

Zr 

Al 

Er 

Y 

Gl 

Mg 

Ca 

Sr 

Ba 

Li 

Na 

K 

Rb 

Cs 



Name. 



Uranium 

BISMUTH 

TIN (Stannum) 

Indium 

LEAD (Plumbum) 

CADMIUM 

Thallium 

COBALT 

NICKEL 

IRON(Ferrum) 

ZINC 

Gallium 

MANGANESIUM .... 

Lanthanum 

Didymium 

Cerium 

Thorium 

Zirconium 

ALUMINUM 

Erbium 

Yttrium 

Glucinum (Beryllium). . 

MAGNESIUM 

CALCIUM 

STRONTIUM 

BARIUM 

LITHIUM 

SODIUM (Natrium). .. 
POTASSIUM (Kalium) 

Rubidium 

Ccv.sium , 



II, IV, VI 

III, V 

II, IV 

Ill 

II, IV 

II 

I, III 

II, (Co,)* 1 

II, (Ni 2 )^....,. 
II, VI, (Fe 2 ) vr ... 
II 

(G«.) VI . 

II, IV, VI, VIII 

III 

III, V 

IV, (Ce 2 ) vr 

IV 

IV 

Ill, or (A1 2 ) VI ... 
Ill, or (Er 2 ) VI ... 

Ill 

II 

II 

II, IV 

II, IV 

II, IV 

I 



POSITIVE END 



Atomic 
Weight. 



238.48 

207.52 

117.69 

113.39 

206.47 

111.83 

203.71 

58.88 

57.92 

55.91 

64.90 

68.85 

53.90 

138.52 

144.57 

140.42 

233.41 

89.36 

27.00 

165.89 

89.81 

9.08 

23.95 

39.99 

87.37 

136.76 

7. 

22.99 

39.01 

85.25 

132.58 



12 PRACTICAL DENTAL METALLURGY. 

To these may be added *Davyum and ^Terbium. 
Some ten or twelve other substances thought to be ele- 
ments are sometimes given, but as their identity has not 
yet been thoroughly established, it is thought better to 
omit them. 

These sixty-six elements are considered under two 
great divisions, which are known as metallic and non- 
metallic. 

METALLIC ELEMENTS, the metals, or, as they 
are frequently termed, the positive elements, are fifty-two 
in number (denoted in the table by the *), and the study 
of these constitutes — 

METALLURGY.— The science of economically ex- 
tracting metals from their ores, and to this strict 
definition may be added the art of applying them to 
useful purposes. 

AN ORE is a substance containing one or more 
metals in their natural state. The metal exists chiefly 
as a sulphide, oxide, or carbonate, and often times as a 
chloride, arsenide, sulphate, phosphate, or silicate. 
Such metals as goM and platinum are usually found in a 
free or metallic state, then they are termed " native." 
Tin, silver, copper, and some other metals are occasion- 
ally found native. 

GANGUE. — The foreign material or impurity in 
which minerals are found embedded is variously 
known as "gangue," "veinstone," or "matrix." This 
may consist of such carbonates as calc-spar, limestone; 
such silicates as feldspar, hornblende, and mica; such 
sulphates as heavy-spar; and such fluorides as fluor-spar. 
This is separated from the mineral by the miner in 
crushing, sorting, and washing operations known as 
"dressing," after which the ore is sent to the metallur- 
gist. 



INTRODUCTION. 13 



SLAG is the refused fused metallic dross or recre- 
ment separated from the metal baring compounds 
when the minerals of iron, copper, silver, nickel, and 
cobalt are fused with arsenic, sulphur, and silica. 
Oxides unite with silica and form a part of the slag. 

REGULUS.— When the minerals of iron^ copper, 
and silver are smelted or fused with substances con- 
taining sulphur the resulting sulphide is known as 
4 ' regulus " or " matte. " 

SPEISS. — When the minerals of nickel and cobalt 
are similarly fused and converted into arsenides 
the combination is termed " speiss." 

REDUCTION is the process of freeing a metal 
from its combinations. The substance effecting this 
result is called a " reducing agent." The chief reduc- 
ing agents are carbon, hydrocarbons, carbon monoxide, 
and hydrogen. In this process metallic compounds are 
usually converted into oxides, if they do not already 
exist as such. This is generally accomplished by heat- 
ing in contact with atmospheric air. For example, when 
zinc carbonate is thus treated the reaction or reduction 
is as follows: 

ZnC0 3 ( + heat)=ZnO + C0 2 . 

Then by addition of the reagent carbon the metallic 
zinc is obtained thus: 

ZnO+C=Zn + CO. 

Sulphides are reduced by partially converting the 
metallic sulphide into an oxide, with the aid of heat, 
when the remaining metallic sulphide reacts with the 
oxide produced, freeing the metal, as for example: 

PbS + 2PbO=S0 2 -!-3Pb. 
These various processes are called " smelting." 



14 PRACTICAL DENTAL METALLURGY. 

ROASTING. — When metalliferous substances are 
reduced to oxides by heating, in contact with atmos- 
pheric air, the process is called "roasting." When 
they are similarly heated in contact with chlorine gas or 
with common salt, the operation is known as "chlorin- 
izing roasting." 

r CALCINATION is the process of heating a sub- 
stance at a temperature below its melting point. 
The object is to expel all volatile and organic matter, 
and, in the ease of ores, to render it more porous prepara- 
tory to roasting or smelting. 

DISTILLATION.— The act of separating the more 
volatile portions of a substance by heat in the form 
of vapor, and subsequently condensing it to a liquid in 
some cooling receiver or worm. Mercury and zinc are 
extracted from their ores by this process, and the former 
metal is purified by redistillation. 

SUBLIMATION is an analogous process, except 
that the substance separated as a vapor is condensed 
as a solid. For example, arsenic is sublimed from ores 
containing it. 

SCORIFICATION is the process of converting the 
foreign substance present in a metallic compound 
into scoria or slag by oxidation and union with silica. 
The vessel in which the operation is effected is termed 
a scorifier. 

OCCLUSION is the property possessed by some 
metals of absorbing and retaining certain gases, thus 
— iron absorbs carbonic oxide readily, silver occludes 
oxygen, platinum will absorb considerable quantities of 
oxygen and hydrogen, and it has been demonstrated 
that palladium foil under certain circumstances will 
absorb 982 volumes of hydrogen. 



INTRODUCTION. 15 



CEMENTATION is the reaction which takes 
place between two substances without fusion. — Thus, 
wheu iron is heated with charcoal — carbon — a reaction 
takes place and the iron is said to become carburized. 
Such a reaction is known as " carburizing cemen- 
tation." 

When iron is heated with red haematite, Fe 2 3 , as an 
oxidizing agent, the impurities contained in it are modi- 
fied or removed by the cement powder. Such a process 
is known as an "oxidizing cementation." 

DRY PROCESS.— The operation of separating 
metals from metallic combinations or metalliferous 
matter by the agency of heat. 

WET PROCESS.— The operation of separating 
metals from metallic combinations or metalliferous 
matter by suitable solvents, such as the ordinary acids, 
etc., and then precipitating those desired with proper 
reagents or by an electrochemical process. 

Of the fifty-two elementary substances known as metals 

only fourteen are employed in their true metallic co?idi- 

tion. These are: 

Iron, Antimony, 

Copper, Magnesium, 

Lead, Bismuth, 

Zinc, Gold, 

Tin, Silver, 

Aluminum, Mercury, 

Nickel, Platinum, 

About twelve are more or less useful in the preparation 
of medicines, in the arts for coloring pigments, and for 
alloying purposes. These are: 

Potassium, Arsenicum, 

Sodium, Chromium, 

Calcium, Cobalt, 

Lithium, Cadmium, 

Barium, Titanium, 

Manganesium, Uranium. 



16 PRACTICAL DENTAL METALLURGY. 

While the remaining twenty-six are more or less rare, 
and as yet of little or no practical value in the metallic 
state. 

The metallurgist groups the metals into two classes, 
which are known as noble and base; 

NOBLE METALS are those whose compounds 
with oxygen are decomposable by heat alone, at a 
temperature not exceeding redness. These are: 

Mercury, Rhodium, 

Stiver, Ruthenium, 

Gold, Osmium, 

Platinum, Iridium, 
Palladium. 

BASE METALS are those whose compounds with 
oxygen are not decomposable by heat alone, retain- 
ing oxygen at high temperatures. 

The base metals are further subdivided with reference 
to their affinity for oxygen and other chemical properties. 

THE FIRST DIVISION 

Contains five metals. They are very readily oxidized, 
and their oxides are all soluble in water, giving it a 
strongly alkaline reaction; so also are their phosphates 
and carbonates, with the exception of lithium phosphate, 
which is quite insoluble, and the carbonate, which is 
only sparingly soluble. They all energetically decom- 
pose water at ordinary temperatures, liberating hydrogen, 
and forming hydrates in solution. They are soft, of low 
specific gravity, and fusible at low temperatures. These 
are: 

Potassium, Rubidium, 

Sodium, Caesium. 

Lithium . 



INTRODUCTION. 17 



THE SECOND DIVISION 

Contains four metals, all of which decompose water at 
ordinal temperatures, except magnesium, combining 
with the oxygen. Their oxides are more or less soluble 
in water, rendering it alkaline; but their neutral carbon- 
ates and phosphates are insoluble. These are: 

Barium, Calcium^ 

Strontium , Magnesia m . 

THE THIRD DIVISION 

Contains thirteen metals, of which but three are of much 
importance. Those which have been isolated do not de- 
compose water at ordinary temperatures without the 
addition of a weak acid or a slight rise of temperature. 
Their oxides and carbonates are insoluble in water. 
These are : 

Aluminum, Erbium, 

Chromium, Cerium, 

Titanium, Lanthanum, 

Glucinum, Didymium, 

Thorium, Tantalum, 

Yttrium, Columbium. 

Zirconium, 

THE FOURTH DIVISION 

Contains nine metals, the chief of which decompose 
water at a red heat. These are : 

Iron, Uranium , 

Nickel, Vanadium, 

Cobalt ', Thallium, 

Manganesutm , Indium. 
Zinc, 



18 



PRACTICAL DENTAL METALLURGY. 



THE FIFTH DIVISION 

Contains four metals, which do not decompose water at 
any temperature. These are : 



Cadmium, 
Lead, 



Bismuth, 
Copper. 



THE SIXTH DIVISION 

Contains six metals. All the higher oxides of these 
metals have acid properties. These are : 

Tin, Molybdenum, 

Antimony \ Tungsten, 

Arsenic, Tellurium. 

The non-metallic elements may be divided according 
to their physical states at ordinary temperatures, thus: 

Gases. 



Oxygen, 


Nitrogen, 


Fluorine. 


Hydrogen, 


Chlorine, 
Solids. 




Carbon, 


Sulphur, 


Phosphorus 


Boron, 


Selenium, 


Iodine. 


Silicon. 


Liquid. 
Bromine. 





CHAPTER II. 

PROPERTIES OF METALS. 

A METAL is an elementary substance, solid at 
ordinary temperatures, with the single exception of 
mercury (a liquid solidifying at — 39° C), having a 
peculiar luster, called a " metallic luster," and the 
property of replacing hydrogen in chemical reac- 
tions, as for example: 

Zn + H 2 S0 4 =ZnS0 4 +H 2 , 

insoluble in water, a good conductor of heat and 
electricity, and possessing the quality of uniting with 
oxygen to form a basic oxide. 

No line can be sharply drawn between metals and non- 
metals; just as none can be drawn between soluble 
and insoluble, poisonous and non-poisonous, substances. 
The two elements, arsenic and tellurium, may well be 
considered the intermediate links between the two classes. 

Sir Henry Roscoe says:* "Arsenic closely resembles 
phosphorus in its chemical properties and in those of its 
compounds, although in physical characters, such as 
specific gravity, luster, etc., it bears a greater analogy 
to the metals; indeed, it may be considered the connect- 
ing link between these two divisions of the elements, 
antimony and bismuth being closely connected with it on 
the one hand, and phosphorus and nitrogen on the other." 

Bloxam evidently does not regard arsenic as a metal. 
Of it he says:f "This element is often classed among 
the metals, because it has a metallic luster and conducts 
electricity, but it is not capable of forming a base with 
oxygen, and the chemical character and composition of 

* Wessons in Elementary Chemistry, p. 148. 
f Chemistry, Inorganic and Organic, p. 272. 



20 PRACTICAL DENTAL METALLURGY. 

its compounds connect it in the closest manner with 
phosphorus." 

Of tellurium Roscoe says:* ' 'Although resembling a 
metal in its physical properties, [it] bears so strong an 
analogy to sulphur and selenium in its chemical relations 
that its compounds are best considered in this place" 
(under the head of non-metallic elements). Again , iodine 
is a crystalline solid, with bright metallic luster, but low 
specific gravity (4.95), and other properties of the non- 
metallic elements. 

Hydrogen, while thought to be a metal, owing to the 
similarity of its chemical properties to other metals, does 
not, at ordinary temperatures at least, present the physi- 
cal qualities of metals. 

All metals, when exposed in an inert atmosphere to a 
sufficient temperature, assume the form of liquids and 
present the following characteristic properties: They are 
practically non-transparent and reflect light in a peculiar 
manner, producing what is called metallic luster. When 
kept in non-metallic vessels they take the shape of a con- 
vex meniscus. When exposed to greater temperatures, 
some sooner, others later, pass into vapors. What these 
vapors are like is not known in many cases, since, as a 
rule, they can be produced only at very high tempera- 
tures, precluding the use of transparent vessels. Silver 
vapor is blue, that of potassium green, and many others 
— mercury, for example — colorless. The liquid metals, 
when cooled down sufficiently, some at lower, others at 
higher temperatures, congeal into compact solids, en- 
dowed with relative non-transparency and the luster of 
their liquids. 

NON-TRANSPARENCY.— Metals as a rule are non- 
transparent, or opaque, yet some have proven to possess 

* Wessons in Elementary Chemistry, p. 131. 



PROPERTIES OF METALS. 21 

the property of transparency in a low degree at least. In 
the case of gold : Through the leaf, or thin films pro- 
duced chemically on glass plate, a light green color is 
transmitted. Also very thin films of mercury are said to 
transmit light with a violet-blue color, and copper, it is 
claimed, is somewhat translucent; while silver in in- 
finitely thin films is absolutely opaque. 

COLOR. — Most metals range from the pure white of 
silver and tin to the bluish hue of lead. Bismuth is a 
light gray, with a delicate tinge of red. Copper is called 
the " red metal." Gold is a rich yellow; barium and 
strontium a straw color, while calcium exhibits a little 
deeper shade. 

LUSTER. — Polished metallic surfaces, like those of 
other solids, divide any incident ray into two parts, of 
which one is refracted, while the other is reflected, with 
this difference, however, that the former is completely 
absorbed, while the latter, in regard to polarization, is 
quite differently affected, which fact, in all probability, 
accounts for the peculiar property of metallic luster. 

ODOR AND TASTE.— Most metals are destitute of 
odor and taste. Peculiar odors are, however, evolved 
from some of them when heated; in fact, one of the means 
of discriminating arsenic consists in its characteristic 
smell of garlic when heated. Iron, copper or zinc when 
heated also evolve peculiar odors. The taste which is 
perceived in some is no doubt due to some peculiar char- 
acter, although in some cases it may depend upon voltaic 
action set up by the chemical agency of the saliva, the 
metal not being perfectly pure. If a piece of zinc be 
placed upon the tongue, and a piece of silver under it, 
and the edges joined, a metallic taste will be perceived 
dependent on slow solution of the zinc under electric 



22 PRACTICAL DKNTAL METALLURGY 

action. The odor, Dr. Kssig says,* " may be noticed in a 
marked degree when holding in the hand a mass of an 
alloy composed of gold, platinum, tin, and silver pre- 
pared for use as amalgam. The moisture of the hand, 
aided by its heightened temperature, seems to promote 
the electrical action." 

CRYSTALLINE FORM.— Most, if not all, metals 
are capable of crystallization, and their crystals belong to 
the following systems: Regular — Silver, gold, palladium, 
mercury, copper, iron, lead; quadratic — tin, potassium; 
rhombic — antimony, bismuth, tellurium, zinc, magnesium. 

Perhaps all metals assume a crystalline structure on 
congealing, differing only in degree of visibility. Anti- 
mony, bismuth, and zinc exhibit a very distinct crystal- 
line structure plainly visible in broken ingots. Tin is 
also crystalline, which fact is evinced by the " tin cry " 
when a bar of the metal is bent, causing the crystal faces 
to slide over one another; but the bar is not easily 
broken, and exhibits an apparently non-crystalline frac- 
ture. Gold, silver, copper, aluminum, cadmium, iron, 
lead, cobalt, and nickel are practically amorphous, the 
crystals being so closely packed as to produce a virtually 
homogeneous mass. 

MALLEABILITY, DUCTILITY, AND TENAC- 
ITY are those properties possessed by some metals by 
virtue of the cohesive power of their molecules, and are 
to that extent kindred. 

Malleability is that quality which admits of a 
metal being hammered or rolled into thin sheets 
without breach of continuity. Many metals possess 
this property relatively, it being most wonderfully ex- 

* Dental Metallurgy, p. 20. 



PROPERTIES OF METALS. 



23 



emplified in gold; leaves of it have been produced the 
1-370, 000th of an inch in thickness, each grain of which 
is capable of covering a square of 75 square inches. 

DUCTILITY is that property possessed by some 
metals by virtue of which they may be drawn into 
wire. The operation consists of forcibly drawing the 
metal through a series of gradually decreasing holes in a 
hard steel draw-plate. Gold is also the most ductile of 
all metals, a single grain of it having been drawn into a 
wire 550 feet in length. This was accomplished by cov- 
ering the gold wire with silver, which is also remarkably 
ductile, thus making a composite wire of greater thick- 
ness. After drawing them to the greatest possible atten- 
uation, the silver was dissolved off by nitric acid, leaving 
a gold wire l-5000th of an inch in diameter. 

These properties, together with that of tenacity, are 
shown relatively for some of the more important metals 
in the following table: 





Malleability. 




Ductility. 




Tenacity. 


1. 


Gold. 


1. 


Gold. 


1. 


Iron. 


2. 


Silver. 


2. 


Silver. 


2. 


Copper. 


3. 


Copper. 


3. 


Platinum. 


3. 


Platinum 


4. 


Tin. 


4. 


Iron. 


4. 


Silver. 


5. 


Cadmium. 


5. 


Copper. 


5. 


Gold. 


6. 


Platinum. 


6. 


Zinc. 


6. 


Zinc. 


7. 


Lead. 


7. 


Tin. 


7. 


Tin. 


8. 


Zinc. 


8. 


Lead. 


8. 


Lead. 


9. 


Iron. 


9. 


Nickel. 






10. 


Nickel. 


10. 


Palladium. 






11. 


Palladium. 


11. 


Cadmium. 







The two properties of malleability and ductility are 
closely related to each other, yet, as may be seen from 
the above table, they do not always parallel each other, 



24 PRACTICAL DENTAL METALLURGY. 

for the reason that ductility in a higher degree than 
malleability is determined by the tenacity of the metal; 
for example, cadmium, though quite malleable, is but 
very slightly ductile, and iron, while ninth in point of 
malleability, is fourth in ductility. In the quality of 
malleability the granular particles of the metal are flat- 
tened and spread in all directions, while in that of 
ductility each granular particle is elongated into a fiber. 
Annealing. — Pure iron, copper, silver, and other 
metals are easily drawn into wire, rolled into sheets, or 
flattened under the hammer. But all these operations 
render the metals harder, and detract from their plastic- 
ity. Their original softness can be restored to them by 
annealing, i. e., by heating them to redness and then 
plunging them into cool water, oil, etc. In the case of 
iron, however, this applies only if the metal is perfectly 
pure. If it contains a few parts carbon per thousand, 
the annealing process, instead of softening the metal, 
gives it a " temper," meaning a higher degree of hard- 
ness and elasticity.* 

Welding. — The process of joining two clean surfaces 
of a metal together by pressure is called welding. This 
property is possessed by iron at white heat, but lead and 
gold will cohere at ordinary temperatures in proportion 
to their purity. Iron may be welded by a current of 
electricity sent through the junction, when the metal is 
heated by the resistance offered to the passage of the 
current. 

Forging. — The process of hammering metals out into 
various shapes. It illustrates the solid flow of metals. 

* See chapter on Iron. 



PROPERTIES OF METAES. 25 

TENACITY is that property possessed by metals, 
in consequence of which they resist rupture when 
exposed to tension. This is ascertained by preparing 
wires of exactly equal diameters and comparing the 
number of pounds weight each will sustain before rupture. 

There are several conditions which materially modify 
the propeities Of malleability, ductility, and tenacity, the 
most important of which are — 

Purity. — Gold is the most malleable of all metals, yet 
if the merest trace of lead, itself a soft metal, be con- 
tained in it, the gold becomes too brittle to be worked, 
and especially is this the case if the gold has any silver 
also with it, as most gold has. This destruction of mal- 
leability and tenacity is yet more pronounced when 
antimony or similar metals are mixed with gold, even in 
minute quantities.* 

Temperature also exercises a very great modifying 
influence over these properties; for example, a bar of 
zinc obtained by casting is exceedingly brittle, but when 
heated to 100° or 150° C. it becomes sufficiently plastic 
to be rolled into thin sheets or drawn into wire. Such 
sheet or wire then remains malleable and ductile after 
cooling. The explanation of this remarkable fact is, 
that the originally only loosely cohering crystals have 
become intertwisted and forced into absolute contact with 
each other, and this is supported by the fact that the 
rolled zinc has a somewhat higher specific gravity than 
the original ingot. If the temperature be carried to 205° 
C it again becomes so brittle that it may be powdered 
in a mortar. Extreme care, therefore, must be exercised 
in the handling of hot zinc dies, for if by accident one be 
dropped upon a hard surface it is likely to be ruined. 

* See chapter on Gold. 



26 



PRACTICAL DKNTAL METALLURGY. 



Aluminum, magnesium, and some other metals, which 
at ordinary temperatures possess little or no ductility, 
may be drawn into wire when heated. 

These qualities are greatly diminished in alloys by 
heating. Some forms of brass, for example, which are 
soft, tenacious, and ductile at ordinary temperatures, are 
made quite brittle by heating to dull redness. Again, it 
is quite certain that 18-carat gold solder is rendered 
brittle at red heat. 

The tenacity of metals in general is greatly diminished 
by heating. The exceptions to this are in the cases of 
iron, steel, and gold. 

The following table shows the results obtained by 
Wertheim* in his experiments on a number of the 
metals at temperatures from 15° to 20° C. 





For Wire 1 Square Mm. Section, Weight 
in (in Kilos) Causing 


Name. 


Permanent Elon- 
gation of 


Breakage. 


Iron, drawn 

" annealed 

Copper, drawn 

Platinum, drawn 

" annealed 

Silver, drawn 

" annealed 

Gold, drawn 

" annealed 

" annealed 

Tin, drawn 


32. 
Under 5. 

12. 
Under 3. 

ll"3 
2.6 
13.5 
3. 

.75 
1. 
.45 
.2 
.25 
.2 


61. 
47. 
40. 
30. 
34. 
23. 
29. 
16. 
27. 
10. 
13. 

*2!45 






Lead, drawn . . 


2.1 


" annealed 


1.8 



* Annales de Chimie et de Physique (III.) Vol. XII. 



PROPERTIES OP METALS. 27 

ELASTICITY.— All metals are elastic to this extent, 
that a change in form brought about by stresses not ex- 
ceeding certain limit values, will disappear on the stress 
being removed. Strains exceeding the "limit of elas- 
ticity " result in permanent deformation, or, if suffi- 
ciently great, in rupture. This property may be in- 
creased in some metals by compounding and alloying. 
Thus, iron compounded with the proper amount of car- 
bon, has its elasticity increased to the very highest 
degree, while the metal itself is almost devoid of the 
quality. The same is true of copper and zinc, in some 
forms of brass, also in gold and platinum; both are soft 
and possessed of little elasticity, yet when combined in 
proper proportions — for example: If 1 part of platinum 
be added to 23 parts of 21-carat gold (alloyed with cop- 
per and silver) an alloy of 20-carat fineness will be pro- 
duced, which will be found to be quite elastic and is 
much used for clasps for artificial dentures. 

SONOROUSNESS.— This is a property possessed by 
the harder metals, and is quite marked in certain alloys, 
such as those of copper and tin, known as bell-metal. Lead, 
which is but feebly, if at all, sonorous, may become so, it 
is claimed, if cast in the shape of a mushroom. Alumi- 
num emits a characteristic sound when struck. The first 
article known to have been made of aluminum was a baby 
rattle for the infant prince imperial of France, for which 
purpose it was well fitted on account of its sonorousness. 
Impurities sometimes increase the sonorousness of a metal, 
as in the case of antimony in lead. 

FUSIBILITY AND VOLATILITY.— All may be 
fused, and most of them are capable of being volatilized, 
but the temperature at which they become fluid differs 
greatly in different metals, as the following table shows: 



28 



PRACTICAL DKNTAL METALLURGY. 



Name of Metal. 


Fusing Point 
Centigrade. 


Fusing Point. 
Fahrenheit. 


Authority. 


Mercury 

Caesium 


39 ^ 

+ 26 to 27! 
30.0 
38.5 
62.5 
95.5 

176. 

180. 

228. 

264. 

290. 

320. 

325. 

415. 

425. 

525. 


—38.2 
+ 78.8 
86. 
101.3 
144.5 
203.9 
348.8 
356. 
442.4 
507.2 
554. 
608. 
617. 
779 
797. 
977. 




Setterberg 

L. de Boisbaudran 

Bunsen 

Bunsen 

Bunsen 

Richter (?) 

( ? ) 


Gallium 

Rubidium 

Potassium 

Sodium 

Indium 

Lithium . 


Tin 


Rudberg 

Rudberg 

Lamy 

Rudberg 


Bismuth 

Thallium 

Cadmium 

Lead 


Zinc 


Person 


Antimony 




Incipient Red Heat 
Magnesium 


Pouillet 


Aluminum 


700. 

700. 
1040. 
1100. 
1100. 
1200. 
1300 to 1400. 

higher-1600. 
1400. 
1600. 

(?) 

1500 to 1600. 
1600. 


1292. 
1292. 
1904. 
2012. 
2012. 
2192. 
2372 to 2552. 

2912. 
2552. 
2912. 

(?) 

2732 to 2912. 

2912. 




Cherry Red Heat . . 

Silver 

Gold 


Pouillet 

Bacquerel 


Yellow Heat 


Pouillet 


Copper 

Iron, wrought .... 
Iron, chemically 








pure 

Cobalt 








Uranium 




Dazzling White 




Heat 


Pouillet 


Palladium 




x y hy d r o g e n 
Flame 






Platinum 


2000. 


3632. 




Iridium 




Rhodium 








Ruthenium 








Max. Temp, of 
xy hy dr ogen 
Flame 


2870. 


5198 






*Bunsen 



Osmium does not melt at 2870°, i. e., is as yet infusible. 



* Jahresb. f. Chem. 1867, p. 41; Phil. Mag. XXXIV, 



PROPERTIES OF METALS. 



29 



Metals maybe characterized as ' fixed" and "volatile." 
Of their volatility we have little precise knowledge. 
The boiling points of a few are given in the following 
table: 



Name of Metal. 


Boiling Point. 


Authority. 


Mercury 

Cadmium 


357.3° C 

860.0° " 

1040.0° " 

Below 1040.0° " 

Above 1040.0° " 


Regnault 

Deville and Troost 


Zinc 

Potassium 


Deville and Troost 
Dewar and Dittmar 



2. 



3. 



For practical purposes the volatility of metals may be 
classed as follows: 

1. Distillable below redness: Mercury. 
Those distillable at red heats : 

Cadmium, Potassium, 

Zinc, Sodium. 

Magnesium, 

Those which are volatilized more or less readily when 
heated beyond their fusing points in open crucibles : 
Antimony (very readily), Tin, 

Lead, Silver. 

Bismuth, 

4. Those which are with very great difficulty volatilized, 
if at all: 

Gold, Copper (?). 

5. Those which are practically ' 'fixed, ' ' or non-volatile: 

Copper {?), Aluminum, 

Iron, Lithium, 

Nickel, Strontium, 

Cobalt Barium. 
Calcium, 

"In the oxy hydrogen flame silver boils, forming a 
blue vapor, while platinum volatilizes slowly, and osmium, 
though infusible, very readily."* 

* William Dittmar. 



30 PRACTICAL DENTAL METALLURGY. 

" It is doubtful, " says Makins, " if it [gold] is volatile 
per se. But if gold be alloyed with copper, it has been 
shown by Napier to be considerably volatalized, so 
that quantities, amounting to 4^ grains, could be col- 
lected during the pouring out of 30 pounds weight from a 
crucible. * * * That mixtures of gold, silver, and 
lead, when cupelled together, volatize considerably." 

SPECIFIC HEAT.— Equal weights of different met- 
als have been found to absorb different amounts of heat 
when subjected to the same temperature. They, indeed, 
possess different capacities for heat. Thus, the amount 
of heat necessary to raise a given weight of water has 
been found to be 31 times as great as that required 
to raise an equal weight of platinum through the 
same interval of temperature; or, in other words, the 
amount of heat required to raise a given weight of 
water through 100° C. will raise 31 times the same 
weight of platinum through 100° C. of temperature. 
Thus, water being taken as the standard or unit, the 
specific heat of platinum is x / 3li or 0.032 that of water. 

TABLE OF SPECIFIC HEATS. 

1. Iron 1138 

2. Nickel 1086 

3. Cobalt . 1070 

4. Zinc 0956 

5. Copper 0952 

6. Palladium . 0593 

7. Silver 0570 

8. Cadmium 0567 

9. Tin 0562 

10. Antimony 0508 

11. Mercury 0333 

12. Gold 0324 

13. Platinum 0322 

14. Lead 0314 

15. Bismuth 0308 



PROPERTIES OF METALS. 



31 



EXPERIMENT No. 1. — Prepare bullets of exactly equal weights of 
several of the above metals, such as zinc, silver, cadmium, tin, and lead; 
expose them to the same temperature, for the same length of time, and then 
drop them simultaneously upon a sheet of wax placed across an open side of 
a pasteboard box. They will be observed to melt their way through or into 
the wax in the order named. 

EXPANSIBILITY.— The expansion of metals by 
heat varies greatly. The coefficient of expansion is 
constant in metals that crystallize in the regular system 
only; the others expand differently in the direction of 
the different axes. To eliminate this source of uncer- 
tainty, these metals are employed as compressed powders. 

The following table gives the linear expansion from 
0° to 100° C, according to Fizeau, the length at 0° being 
taken as unity:* 



Name of Metal. 



Platinum, cast 

Gold, cast 

Silver, cast 

Copper, native 

Copper, artificial , 

Iron, soft , 

Steel, cast 

Bismuth, mean expansion 

Tin, compressed powder 

Lead, cast 

Zinc 

Cadmium, compressed powder, 

Aluminum, cast 

Mercury 



Expansion. 
0° to 100° C. 



.000907 

.001451 
.001936 
.001708 
.001869 
.001228 
.001110 
.001374 
.002269 
.002948 
.002905 
.003102 
.002336 
.018153 



"The high rate of expansibility of zinc renders it par- 
ticularly valuable as a metal for dies upon which to form 
plates for the mouth in many cases. The metal is cast 
while fluid and at its extreme limit of expansion, 
which upon cooling returns to its minimum dimensions, 
and thus furnishes a cast a little smaller than the plaster 
model which it represents. It has been found that this 



* William Dittmar. 



32 



PRACTICAL DENTAL METALLURGY. 



contraction of the zinc die a trifle more than compensates 
for the expansion which takes place in the plaster model 
in setting, and in the majority of cases a plate made 
thereon adapts itself more accurately to the mouth than 
one made upon a die of less expansible metal. Even if 
the contraction undergone by the zinc is so great as to 
produce a die somewhat smaller than the mouth, so far 
from being a detriment, it is a positive advantage in 
most cases of full upper replacement, as under such con- 
ditions the pressure of the finished plate is greater upon 
the alveolar ridge than upon the central portions of the 
hard palate — a state of affairs the advantages of which 
are sufficiently obvious without explanation."* 

CONDUCTIVITY.— Metals are good conductors of 
heat and electricity, but the quality — whether thermic or 
electric — is very differently exhibited in different metals. 
An exact knowledge of these conductivities is of great 
scientific and practical importance to the dentist, and too 
much attention cannot be given their consideration. 

The following table gives the thermic and electric con- 
ductivities of some of the more important metals and 
alloys : 





Relative Conductivity. 


Names of Metals. 


Thermic. 


Electric, at 0° C 


Silver 


100.0 

73.6 

53.2 

14.5 

11.9 

8.5 

8.4 

1.8 

23.6 

11.6 

7.3 

2.8 


100.00 


Copper 


99.95 


Gold 

Tin 

Iron 

Lead 


77.96 
12.36 
16.81 

8.32 


Platinum 


18.80 


Bismuth 

Brass 

Steel 


1.24 


German Silver 


7.67 


Rose Fusible Metal 




Pianoforte Wire 


14.40 







*Dr. E. C Kirk, Am. System of Dentistry, Vol. Ill, p. 793, 



PROPERTIES OF METALS. 



33 



Makins states that amongst the results of Dr. Mat- 
thiessen's experiments upon the electric conductivity of 
metals "are the facts that impurity of a metal or alloy- 
ing it greatly diminishes its conducting power. Rise of 
temperature again has the same effect. Thus between 
32° F. and 212° (or 0°C. and 100°) great diminution takes 
place, and that not uniformly, as some lose it much more 
in proportion than others, by thus raising the tempera- 
ture. Many lose as much as twenty-five per cent, of their 
conducting power." 

An illustration of the comparative conductivity of the 
metals is observed in the incandescent lamps with plati- 
num coils. The electricity is readily transmitted from 
its source by the copper efferent wire, but when it meets 
the platinum that metal offers so much resistance to the 
passage of the current, on account of its low conducting 
power, that it becomes white-heated — incandescent. 

SPECIFIC GRAVITY.— This property varies in dif- 
ferent metals from .594 (lithium) to 22.48 (osmium), as 
the following table shows: 



Name of Metal. 


Specific Gravity. 


Authority. 


Lithium 


.594 
.875 
.9735 
1.52 
1.578 
1.743 
1 88 
2.1 
2.5 
2.583 
Over 4. 
4.15 
5.5 
5.9 


Bunsen 


Potassium 


Baumhauer 


Sodium 


Baumhauer 


Rubidium 


Bunsen 


Calcium 


Bunsen and Matthiessen 


Magnesium 


Bunsen 


Caesium 


Setterberg 
Debray 


Glucinum 


Strontium 


Aluminum 


Mallet 


Barium 


Clarke 


Zirconium 


Troost 


Vanadium 

Gallium 


Roscoe 

Lecoq de Boisbaudran 





{Table continued on following page.) 



34 



PRACTICAL DENTAL METALLURGY. 



TABLE— Continued. 


Name of Metal. 


Specific Gravity. 


Authority. 


Lanthanum 


6.163 
6.544 

6.728 

6.715 
6.81 
6.915 
7.14 
7.29 
7.42 
7.844 
8.279 
8.546 
8.5 
8.6 
8.94 
9.823 
10.4 
11.25 
11.4 
11.86 
12.1 
12.26 
13.595 
16.54 
18.33 
19.265 
21.46 
22.4 
22.477 


Lecoq de Boisbaudran 
f Hillebrandt and 
\ Norton 
j Hillebrandt and 
I Norton 

Marchand and Scheerer 


Didymiuui 


Cerium 


Antimony 


Chromium 


Wohler 


Zinc 


Karsten 


Mansfanesium 


Brunner 


Tin 




Indium 


Richter 


Iron 

Nickel 


Berzelius 
Richter 


Cadmium 


Schroder 


Cobalt 

Molybdenun 

Copper 


Debray 


Eismuth 


Holzmann 


Silver 


Holzmann 


Lead 


Deville 


Palladium 


Deville and Debray 


Thallium 


Crookes 


Rhodium 


Bunsen 


Ruthenium 


Deville and Debray 


Mercury 


H. Kopp 
Wohler 


Tungsten 


Uranium 

Gold 


Peligot 
Matthiessen 


Platinum 




Iridium 




Osmium 


Deville and Debray 







CHAPTER III. 

COMPOUNDS OF METALS AND NON-METALS. 

Metals combine with each other indefinitely to form 
alloys, preserving the metallic appearance and properties. 
They combine with non-metals in definite chemical pro- 
portions to form compounds of a more precise nature, in 
which case the metallic characters are almost invariably 
lost. These definite compounds include the 

Oxides, Fluorides, 

Sulphides, Cyanides, 

Chlorides, Selenides, 

Bromides, Tellurides. 

They also combine with 

Nitrogen, Silicon, 

Phosphorus, Carbon, 

Boron, 

forming nitrates, phosphates, and phosphides, borates, 
etc. 

METALLIC OXIDES.— All metals combine with 
oxygen to form oxides, and most of them in several 
proportions. As a class they exhibit a greater disposi- 
tion to unite directly with oxygen than the non-metals, 
though few of them will do so in their ordinary condition 
and at ordinary temperatures. Several metals, such as 
iron and lead, are superficially oxidized when exposed to 
the air under ordinary conditions, but this would not 
be the case unless the air contained water and carbon 
dioxide, which greatly favor oxidation. Among the 
more important metals, five only are oxidized in dry air 
at ordinary temperatures, viz., potassium, sodium, bar- 
ium, strontium, and calcium. The affinity of these 
metals for oxygen is so great that they must be kept 



36 PRACTICAL DENTAL METALLURGY. 

under naphtha (C IO H I6 ) or some substance containing no 
oxygen. 

EXPERIMENT No. 2.— With a knife cut off a small piece of metallic 
sodium; observe it exhibits a brilliant luster but speedily tarnishes by com- 
bining with the oxygen of the air, forming the oxide (NaO) of sodium. 
Plunge the sodium into a jar of oxygen: it takes fire and burns with a bril- 
liant yellow flame. 

Zinc on the other hand exhibits no disposition to com- 
bine with oxygen at ordinary temperatures, but is in- 
duced to do so at a moderate heat (1040° C. or 1900° F.), 
when it burns with a beautiful greenish flame, produced 
by the union of its vapor with the oxygen of the air, 
forming zinc oxide — ZnO. 

EXPERIMENT No. 3.— With a piece of zinc foil form a tassel, gently 
warm the end, dip into a little flowers of sulphur, kindle, and let down into a 
jar of oxygen, when the flame of the burning sulphur will ignite the zinc, 
which burns with great brilliancy, forming oxide of zinc. 

A large number of the metals are oxidized during 
fusion. I^ead, for example, may be entirely transformed 
into its oxide by continued exposure to sufficient heat. 
The oxides of others may be formed by heating a car- 
bonate or nitrate of the metal to redness. For example, 
if ZnC0 3 be heated to a red heat C0 2 is evolved, leaving 
the pure zinc oxide (ZnO). Again, the oxide of copper 
may be obtained by digesting that metal in nitric acid, — 
3Cu+8HN0 3 =3Cu(N0 3 ) 2 + 4H 2 + 2NO— forming the 
nitrate of copper, which then may be decomposed by 
heat into nitric and cupric oxides. 

They are also formed from some salts; for example, if 
to a solution of sulphate or chloride of iron .ammonium 
hydrate be added the hydrated sesquioxide of iron 
(Fe 2 3 3HO), the antidote for arsenic is formed. And 
zinc oxide may be obtained by adding caustic potassa to 
a solution of zinc sulphate. 

Deflagrating some metals with an oxidizing agent pro- 
duces an oxide of the metal. Advantage is taken of this 



COMPOUNDS OF METALS AND NON-METALS. 37 

in rendering brittle gold malleable by roasting it with 
nitrate of potassium.* The contaminating tin , lead , zinc, 
antimony, etc., are extracted from the noble metal, as 
oxides by the oxygen of the nitrate, and dissolved in the 
molten flux. 

Other metals, such as gold, platinum, iridium, rhodium, 
and ruthenium, do not combine directly with oxygen, 
their combination being effected only by indirect means, 
and with difhculty. 
Oxidizing Agents are substances such as — 
Oxygen (O), Potassium and (KC10 3 ) 

Air (O and N), Sodium Chlorates(NaC10 3 ), 

Water (H 2 0), Iron Tetroxide (Fe 3 4 ), 

Potassium and (KN0 3 ) Iron Trioxide (Fe 2 3 ), 
Sodium Nitrates (NaN0 3 ), Carbon Dioxide (C0 2 ), 
which, imparting a part or the whole of their oxygen to 
another substance, cause it to become oxidized; con- 
versely — 

Deoxidizing Agents are substances such as — 
Carbon (C), Compounds of hydrogen 

Carbon monoxide (CO), and carbon — carbo-hydrides, 
Hydrogen (H), and some times metals, 

which reduce oxides by combining with the oxygen 
which they may contain. 

Examples of oxidation — 
Zn+0=ZnO 

3FeCO s + 0= Fe 3 4 + 3C0 2 
3FeO + C0 2 =Fe 3 4 + CO 

Examples of deoxidation — 

2KC10 3 +C 3 =2KC1 + 3C0 2 
Fe 2 3 +H 6 =Fe 2 +3H 2 
Fe 2 3 + 3CO=Fe 2 + 3C0 2 

* See chapter on Gold. 



38 PRACTICAL DENTAL METALLURGY. 

Substitution or Replacement. — Just as chlorides are 
derived by substitution from hydrochloric acid, HC1, so 
may oxides be represented as being derived from one or 
more molecules of water, H 2 0, by the substitution of a 
metal for hydrogen; with this difference, however, that 
water contains two atoms of hydrogen; therefore, the 
replacement may be only partial, producing the hydra ted 
oxide, or complete, forming the oxide. Thus the mon- 
oxides may be formed by the replacement of both atoms 
of hydrogen by a monad, as Na 2 0, Ag 2 0, or a dyad, CuO, 
ZnO; while the higher oxides may be regarded as two or 
more molecules of water, in which the hydrogen in a 
similar manner is replaced by its equivalent of meta 1 , as 
Mn0 2 , A1 2 3 . 

The oxides may be classed as Basic Oxides and Acid- 
forming Oxides. 

Basic Oxides. — When the replacement of the hydro- 
gen is complete, the resulting compound is a basic 
oxide— K 2 + H 2 0==K 2 + H 2 . 

Hydroxides. — When the replacement of the h3'drogen 
is incomplete, the resulting compound is a hydroxide — 
K+H 2 0=KH0 + H, or with the dyad calcium, Ca + 
2H 2 0=Ca2HO+H 2 . 

Bases neutralize acids either partially or entirely, 
replacing either a part or all of their hydrogen, thus we 
have KHS0 4 and K 2 S0 4 . 

An Alkali is only a particular species of base, and might 
be denned as a base which is very soluble in water, as 
K 2 and Na 2 0. 

It will be observed that metals are capable of form- 
ing bases by combining with oxygen, or salts by com- 
bining with salt-radicals. Many metals,* however, form 
acid-forming oxides or anhydrides; thus tin forms stannic 

* See Sixth Division, Chapter I. 



COMPOUNDS OF METALS AND NON-METALS. 39 

anhydride (SnOJ, and antimony forms antimonic anhy- 
dride (Sb 2 5 ), and it is always found that the acid-form- 
ing oxide of a metal contains a larger proportion of oxy- 
gen than any of the other oxides which the metal may 
happen to form, thus: 

The Acid-forming Oxides are those metallic oxides, 
or anhydrides which form acids with water, as in the 
case of non-metallic oxides. 

A number of metallic oxides are found in nature as 
ores from which the metals are reduced. Tin occurs as 
tinstone, Sn0 2 , iron as Fe 2 3 , and Fe 3 4 , etc. 

REDUCTION OF METALLIC OXIDES.— The 
variable affinities exhibited by the metals for oxygen 
groups them into two classes already known as noble 
and base metals. 

Reduction of the Oxides of the Noble Metals. — So 
feeble is the affinity of the noble metals for oxygen that 
their oxides are easily decomposed and the metals 
reduced without the aid of any other agency than that of 
simply heating to redness — about 600° F. 

Reduction of the Oxides of the Base Metals. — On the 
other hand the base metals exhibit a very strong affinity 
for oxygen and the mere application of heat will not 
reduce them, indeed, in many instances a decided 
increase of temperature serves only to strengthen their 
affinity and hence increase the proportion of oxygen 
in the compounds previously formed. Therefore, in 
addition to heat the assistance of some substance is 
required whose affinity for oxygen is stronger than that 
of the metal and will, when favored by heat, abstract the 
oxygen from the oxide. Thus, the oxide of lead may be 
formed by heating the carbonate: 

PbC0 3 (+ heat)=PbO + C0 2 , 
and driving off the carbon dioxide (C0 2 ). The lead 



40 PRACTICAL DENTAL METALLURGY. 



oxide (PbO), however, cannot be further reduced to 
metallic lead by heat; on the contrary, if the heating be 
continued, the production of a higher oxide only will 
be effected. But if, in addition to heating, the oxidized 
lead be covered with a layer of pulverized charcoal, 
which will abstract the oxygen for its own conversion 
into carbon dioxide, the lead will be reduced or liberated. 
Such a reduction is accomplished by the reducing or 
deoxidizing agent, carbon favored by heat: 
2PbO + C (+heat)=2Pb+C0 2 . 

When the lead or zinc used for counter-dies and dies 
in the laboratory are overheated or subjected to frequent 
or long continued meltings, they become partially 
oxidized and covered with an earthy looking mass con- 
sisting of partially oxized metal. A continued exposure 
to heat would, as we have observed, have the effect of 
converting this into an oxide of a higher degree, but if 
the molten metal be covered with pulverized charcoal 
(C) or other carbonaceous substance, such as oil, 
fat, suet, or scraps of beeswax (hydro-carbons), the 
oxygen of the oxide will be abstracted, carbon dioxide 
formed and evolved, while the metal will be reduced to a 
free state. 

Reduction with Hydrogen. — Other oxides which 
cannot be reduced by deoxidizing agents favored by the 
conditions as stated above may, by the assistance of 
proper apparatus and heat, be reduced by a current of 
dry hydrogen. 

EXPERIMENT No. 4. — Pass the delivery-tube of an ordinary hydrogen 
generator (A, Fig. 1) into one end of a drying tube (B), well filled with frag- 
ments of calcium chloride, for the purpose of absorbing the moisture which 
may be carried over with the gas; connect the other end of the drying tube 
with a tube (C) upon which a bulb (D) has been blown for the reception of the 
metallic oxide. After the gas has completely driven the air out of the appara- 
tus, heat is applied to the bulb containing the oxide. As the dry hydrogen 



COMPOUNDS OF MF/TALS AND NON-METALS. 



41 



flows over the heated oxide in a strong stream it combines with the oxygen — 
favored by heat — and passes out of the tube (E) as aqueous vapor, while the 
metal is left free. 




Fig. 1. 



Reduction with Sulphur. — Some oxides may be best 
reduced by beating with sulphur, in which case sulphur 
exhibits a greater affinity for the oxygen than the metal 
does, and, abstracting it, forms sulphur dioxide (S0 2 ). 
A portion of the sulphur, however, combines with the 
metal, converting it into a sulphide or sulphate, or a 
mixture of both. The reduction of such compounds is 
treated under metallic combinations with sulphur. 

Reduction with Chlorine. — There are a few oxides 
which may be reduced by chlorine gas. Thus platinum 
oxide is reduced in a current of dry chlorine. 

EXPERIMENT No. 5.— Repeat experiment No. 4, using calcium oxide 
in the drying tube, and dry chlorine gas. 

METALLIC SULPHIDES.— Metals combined di- 
rectly with sulphur to form a class of compounds which, 
in a chemical and economical point of view, are almost 
as important as the oxides, since the ores of many of the 



42 



PRACTICAL DENTAL METALLURGY. 



most important metals are found as sulphides, for ex- 
ample, galena (PbS); stibnite (Sb 2 S 3 ); zinc-blende (ZnS); 
greenockite (CdS); copper-glance (CuS); iron pyrites 
(FeS 2 ); cinnabar (HgS); silver glance (Ag 2 S), etc. 
These are generally brittle solids possessing so high a 
degree of luster that some of them have been mistaken 
for gold, hence iron pyrites has been called ''fool's 
gold." In composition they resemble the oxides and 
hydroxides, with many of which they are analogous. 
The exceptions to this analogy being the alkalis and 
alkaline earths, there being but two oxides of potassium, 
sodium, and barium, while there are no less than five 
sulphides of these metals. All the metallic sulphides 
are solid at ordinary temperatures; most of them fuse at 
red heat, and some sublime unchanged. When roasted 
in air at high temperatures they are converted into sul- 
phates; (ZnS + 4 favored by high heat=ZnS0 4 , or, if 
they are exposed to higher and continued heat, into 
oxides. 

They may be prepared by heating the metals or their 
oxides with, sulphur, from the sulphates by heating them 
with charcoal, deoxidizing them, and from their soluble 
salt solutions by adding sulphuretted hydrogen: 



EXPERIMENT No. 6.— To the following salt solutions in several test- 
tubes add a few drops of sulphuretted hydrogen: 



Pb2C 2 H ;J 2 + 


H 2 S = 


PbS+ 2HC 2 H 3 2 


Lead acetate 




Lead sulphide 
(Black) 


2AsCl 3 + 


3H 2 S = 


ASoS 3 + 6HC1 


Arsenious 




Arsenious 


Chloride 




Sulphide 
(Lemon yellow) 


Cd2NO,,+ 


H.,S = 


CdS+ 2HNO r , 


Cadmium 




Cadmium 


Nitrate 




Sulphide 
(Yellow) 



COMPOUNDS OF METALS AND NON-METALS- 43 



2SbCl 5 + 5H 2 S = 


Sb 2 S s + 10HC1 


Antimonic 


Antimonic 


Chloride 


Sulphide 




(Orange yellow) 


Zn2C 2 H 3 2 + H,S= 


ZnS+ 2HC 2 H 3 2 


Zinc acetate 


Zinc sulphide 




(White) 


HgCl 2 + H 2 S = 


HgS+ 2HC1 


Mercuric chloride 


Mercuric sulphide 




(1st White) 




(2d Yellow orange) 




(3d Brown) 




(4th Black) 



REDUCTION OF THE METALLIC SUL- 
PHIDES. — Since the ores of many of the most impor- 
tant metals are sulphides, and it is from such compounds 
that we derive our chief supply of copper, lead, mercury, 
silver, antimony, and several other metals, the subject of 
their reduction is of great importance. 

Reduction by Heat. — The reduction of some of the 
metallic sulphides, such as gold, platinum, silver, and 
mercury, is effected by heat alone. The oxygen of the 
air unites with the sulphur, which is evolved as sulphur 
dioxide, S0 2 . In some instances, however, a portion of 
the oxygen combines with the metal, and an oxide 
instead of the free metal is obtained. In some cases the 
sulphide is oxidized and converted into a sulphate, 
which, in turn, may be decomposed at high tempera- 
tures, separating into sulphur dioxide and free metal, or, 
at times, a metallic oxide. Then, again, some of the 
sulphides may, when roasted in air, be converted into 
permanent sulphates capable of resisting high degrees 
of heat. 

Reduced with Iron. — Iron exhibits a strong affinity 
for sulphur and when favored by heat will abstract it 
from several metals, such as silver, lead, etc. Thus, if 



44 PRACTICAL DENTAL METALLURGY. 

the sulphide of lead (galena) be heated with scraps of 
iron, metallic lead is freed : 

PbS-f-Fe=FeS + Pb 
or in the case of silver : 

Ag 2 S+Fe=FeS + 2Ag. 
Rsduced with Hydrogen. — The sulphides of such 
metals as antimony, bismuth, copper, tin, and silver are 
decomposed by passing a current of dry hydrogen over 
them at a red heat, the metal being reduced, while the 
hydrogen combines with the sulphur, forming sulphu- 
retted hydrogen : 

CuS + 2H=H 2 S+Cu. 

Reduced with Chlorine. — Dry chlorine gas also 
decomposes some metallic sulphides, combining with 
both metal and sulphur. 

Reduced with Acids. — Nitro-hydro chloric acid con- 
verts the sulphides into chlorides, and hydrochloric acid, 
in a few instances, acts similarly: its hydrogen combining 
with the sulphur is evolved as sulphuretted hydrogen. 
Strong nitric acid also decomposes them, the sulphur 
being oxidized and the liberated metal combines with the 
acid to form a nitrate. Mercuric sulphide is the only 
one that can not be thus reduced. 

METALLIC CHLORIDES.— All metals combine 
with chlorine, and some of them in several proportions; 
thus we have stannous (SnClJ and stannic chlorides 
(SnCl 4 ). 

Some of the chlorides occur in nature, those of silver 
(AgCl) and mercury (Hg 2 Cl 2 ) as minerals, and those of 
sodium and potassium in enormous quantities in the solid 
state and dissolved in waters. 

They may be regarded as derived, like the oxides, from 
a type — HC1 — substituting for the hydrogen of one or 



COMPOUNDS OF METALS AND NON-METALS. 45 

more molecules of hydrochloric acid an equivalent in 
metal, thus: 

From HC1 are derived monochlorides like KC1. 

" H 2 C» 2 " " dichlorides " SnC1 2 . 

" H3CI3 " " trichlorides " AuCl 3 . 

" H 4 C1 4 " " tetrachlorides " SnC) 4 . 
Preparation. — They may be prepared by the action of 
hydrochloric acid upon the metals. Zinc, tin, cadmium, 
iron, nickel, and cobalt may be readily dissolved by 
hydrochloric acid, forming chlorides respectively and 
liberating hydrogen: 

Zn+2HCl=ZnC1 2 +H 2 

They are also prepared by the action of nascent chlo- 
rine developed by the mixture of nitric to an excess of 
hydrochloric acid. Gold and platinum are dissolved in 
this mixture (aqua regia) and stannic chloride is formed 
by its action on tin. 

Some are also prepared by subjecting the metal or its 
oxide to a current of dry chlorine gas. In this manner 
the chlorides of titanium, aluminum, and chromium may 
be formed. 

Sometimes a chloride is prepared by the substitution 
of one metal for another, thus stannous chloride may be 
made by distilling metallic tin with mercuric chloride: 

HgCl 2 + Sn=SnCl 2 + Hg. 

Other chlorides may be prepared by dissolving the 
oxides, hydroxides, or carbonates of the metals in hydro- 
chloric acid. 

REDUCTION OF METALLIC CHLORIDES — 
The chlorides of gold and platinum may be decomposed 
by heat alone. Gold possesses so feeble an affinity for 
chlorine that solutions of the chloride of gold may be 
decomposed by mere exposure to light or atmospheric 



46 PRACTICAL DENTAL METALLURGY. 

air. Solutions of sugar, gum arable, oxalic acid, etc., 
readily decompose it.* 

Silver chloride yields pure silver and emits an odor of 
hydrochloric acid when heated strongly on charcoal. 
When placed in water acidulated with hydrochloric or 
sulphuric acid, silver chloride may be reduced by stirring 
with small pieces of iron or zinc; the reaction is as fol- 
lows: 

Fe+H 2 S0 4 =FeS0 4 +H 2 , and 

2H-f2AgCl=2HCl+2Ag.t 

With the exception of the chlorides of the alkalis and 
alkaline earths all other chlorides may be decomposed 
by heating them in a current of hydrogen, hydrochloric 
acid and the pure metal being the result; but the evolu- 
tion of the hydrogen must be well maintained, in order 
to drive off the hydrochloric acid formed, or it will react 
with the pure metal, forming fresh chloride. 

Some chlorides may be decomposed by heating them 
with a metal which has a more powerful affinity for 
chlorine; thus, aluminum chloride may be reduced by 
heating it with sodium. 

Sulphuric acid decomposes some chlorides and con- 
verts them into oxides, the oxygen being supplied by 
the water present. 

METALLIC BROMIDES.— Bromine, though less 
active than chlorine, unites directly with most of the 
metals, forming compounds analogous to the chlorides 
and resembling them closely in general properties. 

A silver bromide (Ag Br) analogous to the chloride 
is found as a natural mineral. Nearly all bromides are 
soluble, and those of the alkali metals are found abun- 
dantly in sea water and in many saline springs. 

*See chapter on Gold. 
f See chapter on Silver.. 



COMPOUNDS OF METALS AND NON-METALS. 47 

REDUCTION OF METALLIC BROMIDES.— The 

bromides are decomposed by oxidizing agents with 
liberation of bromine. The affinity of bromine for the 
metals being inferior to that of chlorine, the latter will, 
with the aid of heat, displace the bromine and form 
chlorides, but bromine can not be displaced in a like 
manner by iodine: 

KBr + Cl=KCl + Br. 

METALLIC IODIDES.— Many metals unite directly 
with iodine, forming compounds analogous to the 
chlorides and bromides. The iodides of potassium and 
sodium exist abundantly in sea water and in some 
springs, and the iodide of silver occurs as a natural 
mineral. Most of them are soluble in water, lead iodide 
being only slightly so, while the iodides of mercury and 
silver are quite insoluble. 

A few of them, gold, silver, platinum, and palladium, 
are decomposed by heat alone, giving up their iodine. 
Ozone promptly decomposes all iodides, while atmos- 
pheric oxygen decomposes those of iron and calcium 
slowly. The superior affinity of chlorine and bromine 
enables these elements to displace iodine and form 
analogous chlorides or. bromides: 

KI+Cl=KCl-fI, or 
KI + Br=KBr + I. 

METALLIC FLUORIDES are formed by heating 
certain metals in the presence of hydrofluoric acid ; by 
the action of that acid on metallic oxides; by heating 
electro-negative metals, such as antimony, with the 
fluoride of lead or mercury. Volatile metallic fluorides 
may be prepared by heating fluor-spar with sulphuric 
acid and the oxide of the metal. With some metals 
fluorine occurs as a natural mineral, as with calcium 



48 PRACTICAL DKNTAL METALLURGY. 

(CaF 2 ), and the double fluoride of aluminum and sodium 
(A1 2 F 6 , 6NaF). 

The fluorides are devoid of metallic luster; most of 
them are easily fusible, and for the most part resemble 
chlorides. 

METALLIC CYANIDES are formed by the union 
of metals with the compound radical cyanogen, CN. 
Potassium and some other metals are converted into 
cyanides by heating them in cyanogen gas or the vapor 
of hydrocyanic acid. 

Cyanides very closely resemble the chlorides, bromides, 
iodides, and fluorides. 

METALLIC SELENIDES— The element selenium 
very closely resembles sulphur in its chemical properties; 
hence, it combines with metals in much the same manner. 
Native selenides are rarely found. 

REDUCTION BY ELECTRICITY.— Probably the 
most powerful means of reducing metals from their com- 
binations with non-metallic elements is obtained through 
the agency of electricity. To accomplish this, a solution 
of the metallic salt is subjected to the action of the 
galvanic current, and decomposed thereby. This is 
simply and beautifully demonstrated by hanging a strip 
or coil of zinc in a solution of lead nitrate. After a few 
hours the zinc passes into solution, and exquisite crystals 
of lead have taken its place. 

The electric furnace of Eugene H. and Alfred H. 
Cowles, of Cleveland, Ohio, has greatly advanced the 
production of such metals as aluminum from corundum, 
boron from boracic acid, and silicon from quartz. The 
furnace is constructed in the form of a rectangular box 
of fire-resisting material, lined with a mixture of fine 
charcoal and lime. It has a removable cover, which is 
perforated with openings to allow the escape of gases 



COMPOUNDS OF METALS AND NON-MKTALS. 49 

evolved. In the sides of this furnace the electrodes — two 
plates of gas carbon — are let in by means of which a 
current of a powerful dynamo-electric machine is intro- 
duced. The charge consists of the coarsely crushed 
ore and coke fragments. The essential feature of the 
process consists, therefore, in employing in the furnace a 
substance like carbon, whose high resistance to the 
passage of the current causes the production of a pro- 
digiously high temperature; and which, at the same time, 
is capable of exercising a powerful reducing action on 
the ore. 



CHAPTER IV. 
MELTING METALS. 

REFRACTORY MATERIALS.— Furnaces designed 
to withstand the strain of high temperatures should be 
lined inside with a material capable of withstanding the 
heat and scorifying action of the material operated upon, 
without melting or decomposing. Such materials are 
either used in the natural state, such as sandstone or 
quartz, oxides of iron, and fire-clay, or they are prepared 
by certain methods. 

Refractory materials are divided into three classes 
with reference to their reaction: ist, those of acid char- 
acter, such as ganister and Dinas clay; 2d, neutral, such 
as fire-clay, chrome ironstone, and graphite; jd } basic, 
such as dolomite, bauxite, alumina, etc. Such sub- 
stances are termed acid, neutral, or basic when the acid 
present is greater, equal to, or less in equivalence than 
the base,* 

Fire-bricks are usually made of fire-clay mixed with 
burnt clay and white sand, which prevent the bricks 
cracking and do not increase the fusibility. The com- 
position differs with the purposes for which they are 

* Ganister is composed of Si0 2 89.5, Al 2 3 4.8, Fe02.8, CaO.l, K 2 0.1, H 2 02.2. 

Dinas Clay = Si0 2 98.3, Al 2 O s .7, FeO.2, CaO.2, K 2 0.1, H 2 0.5. 

Kaolin, which is the purest form of fire-clay, contains Si0 2 40, Al 2 3 45, 
H 2 015. 

Dolomite = CaC0 3 and MgC0 3 . In this case the carbon dioxide is removed 
by heat, leaving the oxides of calcium and magnesium, which are entirely 
basic. 

Bauxite = Al 2 O s 52, Fe 2 3 27.6, H 2 20.4. 

Fire-clays are essentially hydrated silicates of alumina, which resist 
exposure to high temperatures without melting or softening. They contain 
varying amounts of lime, magnesium, oxide of iron, potash, etc., and some 
mechanically mixed silica. 

Graphite (Cumberland) = C 91.55, volatile matter 1.1, ash 7.35. 

Hiorns. 



MEI/TING METALS. 51 

designed — some are required to withstand high and pro- 
longed temperatures without softening; some to with- 
stand great pressure; some to resist the corrosive action 
of metallic oxides, and others to withstand great and 
sudden changes of temperature. 

Crucibles. — These are vessels made of various 
mixtures of clay, in the raw and burnt state, mixed 
with coke dust or plumbago, and are designed for 
calcining or fusing substances which require high 
temperatures. 

A good crucible should be tough, infusible, capable of 
withstanding sudden changes of temperature without 
fracture, and should not be readily corroded by metallic 
oxides. The most infusible crucibles are those made 
with clays containing the largest amount of silica, and 
the smallest quantity of calcium and iron oxides. A 
good crucible may be made with two-thirds fire-clay and 
one-third burnt fire-clay and coke dust, which prevent it 
being distorted when burnt. The power of resisting 
corrosion may be tested by melting copper in the crucible 
and adding a little borax. The latter unites with any 
copper oxides that may be formed, and will corrode the 
crucible rapidly unless it is of good quality. 

Graphite, black-lead, or plumbago crucibles are made 
of fire-clay mixed with varying proportions (25 to 50 
per cent.) of plumbago or coke dust. The best ones are 
made with purified plumbago, as the natural material 
often contains impurities in the ash which would act 
injuriously in the clay. Instead of using black-lead 
crucibles, clay ones lined, or " brasqued " with charcoal 
paste are often employed. The graphite crucible is the 
most enduring of all crucibles, but they should never be 
used in melting or alloying noble metals without first 
being tested by subjecting them to a red heat, as a crack 



52 PRACTICAL DENTAL METAIJJJRGY. 

or other imperfection may exist that escapes the notice 
while the vessel is cold. Again, bubbles of air or parti- 
cles of organic substances occasionally become mixed 
with the material, which, upon being heated, cause the 
crucible to be broken, thereby risking the loss of the 
metal. 

There are a variety of clay crucibles, the most impor- 
tant of which are: ist, French — -Of excellent quality, 
smooth, carefully made, but somewhat brittle; 2d, 
London — Close-grained, reddish-brown, refractory, and 
resist well the corrosive action of metallic oxides; $d y 
Cornish — Quite refractory, but are of a more acid char- 
acter than the preceding, and hence are more readily 
attacked by metallic oxides; 4th, Hessian — These are 
exceedingly useful, refractory, not readily corroded. 
They are composed of SiO 2 70.2, Al 2 3 24.8, Fe 2 3 3.8. 
They may be used for rough fusions, but when precious 
metals or their alloys are to be fused in them they should 
be first thoroughly lined with a surface of borax, or the 
rough, porous sides will absorb a considerable portion of 
the molten metal. Being of acid character, they are also 
subject to corrosion by basic fluxes, with which they 
form fusible compounds. They are well adapted to the 
fusion of noble metals where no fluxes are introduced 
for chemical action. Though they do not show a great 
resistance to extreme heat, they are very slightly affected 
by sudden alterations in temperature, as they may be 
plunged cold into a strongly heated furnace, or, white- 
hot, into cold water, without cracking. The Cornish 
crucible, though very similar to the Hessian variety, is 
not quite so rapidly perforated by corrosive fluxes. 

Crucibles are also made of porcelain, gold, silver, 
platinum, iron, etc., but their use is confined almost 
entirely to the chemical laboratory. 



MELTING METALS. 53 



Platinum is fused either in a crucible of gas carbon or 
in. a concavity carved in a block of quicklime, the latter 
of which forms part of the furnace described in the 
chapter on platinum. 

FLUXES are certain fusible substances which, 
when heated with metalliferous matter, assist in the 
fusion and aggregation of the metallic globules by 
cleansing and protecting them from foreign matters, 
such as gangue, oxides, sulphides, chlorides, etc. 

With these foreign substances the flux forms a fusible 
slag from which the metals held as oxides, sulphides, 
chlorides, etc., may be subsequently reduced. 

Like the refractory materials, fluxes may be classified 
as acid, neutral, and basic in their reaction. Thus, when 
gold quartz is fused with sodium carbonate, the quartz, 
a siliceous or acid gangue, reacts with the carbonate 
forming sodium silicate, liberating carbon dioxide, and 
separating the gold which is held mechanically. 

A number of fluxes are used for the specific purpose of 
removing certain impurities or debasing elements from 
molten metal. This they accomplish in two ways- — first, 
by acting as simple solvents for the impurity, as mentioned 
previously, and forming a slag; second, by forming com- 
pounds, such as oxides, sulphides, chlorides, etc. with 
the debasing elements, which are either volatile or solu- 
ble in the molten flux. Others act in a reverse manner; 
these are reducing agents, the function of which is to 
reduce to a metallic state such metallic oxides as are dis- 
solved in the molten metal, and which confer friability or 
brittleness upon the metal when cast. 

The following may be enumerated as the fluxes of 
most common application, with their uses denned: 

Borax, sodium tetraborate, Na 2 B 4 7 , 10B 2 O. This 
salt is of almost universal use, but should be first fused 



54 PRACTICAL DENTAL METALLURGY. 

to drive off its tea parts water of crystallization, and the 
glassy mass thus obtained is to be powdered. When 
highly heated it is of acid reaction, combining with metal- 
lic oxides to form borates; at lower temperatures it takes 
up foreign matters generally, setting the metal free and 
so cleansing its surface as to allow of complete aggrega- 
tion of the particles into a button form. It is found 
native in abundance in California, Europe, Peru, and 
other localities. It is also artificially prepared by neu- 
tralizing boric acid with soda ash. 

Sodium Carbonate, Na 2 C0 3 , 10H 2 O. This salt may be 
preferred to potassium carbonate from the fact that the 
latter is quite deliquescent. It decomposes silicates, as 
already instanced, and much easier when charcoal is 
present. It forms fusible compounds with metallic oxides 
and decomposes some chlorides, for example, silver 
chloride. 

Potassium Carbonate, K 2 C0 3 , is quite similar to the 
sodium salt; it dissolves the earthy impurities, with 
which it forms an exceedingly liquid flux, thus enabling 
the heavier particles of metal to sink through the fluid 
mass and collect in a button at the bottom of the crucible. 

Potassium Nitrate, saltpetre, nitre, KN0 3 , is an 
exceedingly useful flux in the purification of noble 
metals. When used as a flux, and heated, it energeti- 
cally gives up a portion of its oxygen to base metals 
which are thus oxidized, and the alkaline nitrate becomes 
a nitrite. 

Sodium Chloride, NaCi, powdered and heated, to 
prevent its decrepitation, is sometimes added to molten 
substances which induce much ebullition, in order to 
check the latter and protect the substance operated upon 
from the action of atmospheric oxygen. Like amnionic 
and mercuric chloride, it forms chlorides with some metals. 



MELTING METALS. 55 



Black Flux, a mixture of potassium carbonate and 
pulverized charcoal, is an excellent reducing agent and 
assists in the fusion of substances. 

Lime, Silica, and Alumina, or lime with the silicate 
of aluminum, are employed together; the silica to 
abstract certain bases by forming with them fusible 
silicates; while the two bases, lime and alumina assist in 
the fusion of the silicates thus formed. A single silicate 
with one base is generally less fusible than a double or 
multiple silicate with two or more bases — hence the two 
bases, lime and alumina, are used with the silica. 

Plumbic, Cupric and Ferric Oxides are used as 
fluxes in some metallurgical operations; the first forming 
an alloy of lead and silver; the copper oxide for 
purifying gold and the ferric oxide as a flux for silica. 

Many prepared fluxes have been introduced from time 
to time for dental soldering operations, but none possess 
any great advantage over pulverized dehydrated borax. 

Dr. H. A. Parr has prepared a very useful, efficient, 
and convenient flux powder; and also a flux wax which 
affords a means for holding clasps, teeth, and other metal- 
lic parts together while they are being invested, and also 
for conveniently fluxing the surfaces to be soldered; the 
latter is obviously accomplished by burning out the wax, 
the flux which it carries remaining. 

A liquid flux used by jewelers and found useful in 
dental solderings is made by dissolving equal parts of 
borax and boric acid in about sixteen parts of water. 

FUEL. — Combustible substances that may be 
quickly burned in air, producing heat capable of being 
applied to economic purposes. 

Fuels are chiefly compounds of carbon and hydrogen, 
known as hydrocarbons. Most of them contain other 
elements, but are essentially carbon and hydrogen. If 



56 PRACTICAL DENTAL METALLURGY. 

oxygen is contained the proportion of hydrogen may be 
equal to, or greater than, but never less than that required 
to form water with oxygen. 

Calorific Energy. — The amount of heat a unit weight 
of a body is capable of yielding when completely burned. 
It is usually measured by the number of the units of 
weight of water it will raise one centergrade degree of 
temperature. 

Thus in the subjoined table the calorific energy of 
wood charcoal, for example, is given as 8080, that is to 
say, one pound of wood charcoal when completely 
oxidized to carbon dioxide will yield sufficient heat to 
raise 8080 pounds of water through one centergrade 
degree; so with the other substances composing the 
table. 

The calorific energy of a fuel containing carbon, hydrogen, 
and oxygen is the sum of the calorific energies of the carbon 
and that of the disposable hydrogen* 

* Disposable Hydrogen. — The amount of hydrogen which may be com- 
bined with oxygen is not available as a source of heat, and is called "non- 
disposable " hydrogen; the excess of hydrogen over the amount which may be 
combined with oxygen being available is called " disposable " hydrogen. 

EXAMPLE No. 1 . — Determine the calorific energy of marsh gas (CH 4 ). 
C = lxl2=12 (The atomic weight of carbon is 12). 
H 4 =4x 1= 4 (The atomic weight of hydrogen is 1). 

CH 4 = 16 (The molecular weight of marsh gas). 

In one pound of CH 4 there is then Jf or y A lb. of 
carbon, the calorific energy of carbon is 8080 
(see table) hence: %x 8080= 6060.0 

In one pound of CH there is T % or ty lb. of hydro- 
gen, the calorific energy of hydrogen being 
34462 % x 34462= 8615.5 



Therefore the calculated calorific energy of marsh gas is 14675.5 

EXAMPLE No. 2. — Determine the calorific energy of defiant gas (C 2 H 4 ). 

EXAMPLE No. 3.— Determine the calorific energy of ethine (C 2 H 2 ). 

EXAMPLE No. 4.— Determine the calorific energy of alcohol (C 2 H 5 HO). 

EXAMPLE No. 5.— Determine the calorific energy of bisulphide of car- 
bon (CS 2 ). 



MELTING METALS. 57 

The experimental and calculated calorific energies of 
substances do not agree. This is probably on account 
of the heat absorbed in their decomposition. 

The calorific energies of different substances obtained 
experimentally, by the method mentioned previously, is 
given in the following table: 

TABLE OF CALORIFIC ENERGIES. 

Hydrogen Burned to water, H 2 34462 

Carbon (wood charcoal) " " Carbon dioxide, CO„ 8080 

" " " " " " monoxide, CO 2474 

Silicon " " vSilicic anhydride, Si0 2 7830 

Phosphorus " " Phosphoric anhydride P 2 5 5747 

Sulphur " " Sulphurous anhydride, S0 2 .. .. 2140 

CARBON COMPOUNDS. 

Marsh gas, CH 4 Burned to C0 2 and H,0 13063 

Olefiant gas, C 2 H 4 " " " " " 11857 

Illuminating gas, H, CO, CH 4 , 



C 2 H 4 , C 6 H 6 , etc. 

Crude petroleum 

Wax 

Tallow 

Alcohol 



" about 12000 

" 10190 

" 10496 

" 9000 

" 7183 

Carbon monoxide " " " 2403 

Calorific Intensity is the pyrometric degree of heat 
obtained when a substance is completely burned. 

Pyrometry is the measurement of high temperatures, 
and is accomplished by means of an instrument called a 
pyrometer. 

The fuels most used in dental laboratories are: wood, 
coal, charcoal, coke, petroleum, gasoline, and coal gas. 

Coal is variously classified, usually into four varieties: 
anthracite, bituminous, cannel r and lignite. Of these 
only anthracite is suitable for dental use. It is the 
nearest approach to pure carbon (about 90 per cent 
carbon); it burns with a small flame, intense heat, and 
no smoke. It should be carefully selected, clean, free 
from slate, and not yield a fusible ash. 

Charcoal is obtained by heating wood to the temper- 
ature of from 350° to 400° C out of contact with the air, 



58 PRACTICAL DENTAL METALLURGY. 

thus the water, acetic acid, tar, and various gases are 
driven off, leaving a black, sonorous, hard mass known 
as wood charcoal. This is of two classes, hard and soft 
wood charcoal, the former being best adapted to dental 
purposes, is made from the beech, oak, alder, birch, 
elm, etc. The soft variety is made from the pine, 
larch, linden, willow, and poplar. Charcoal is particu- 
larly indicated for dental use for maintaining high tem- 
peratures in a small compass. It should be kept 
protected from moisture, which it will absorb, impairing 
its calorific energy. 

Coke is a carbonaceous residuum obtained when coal 
is strongly heated in a closed space with a limited supply 
of air, the volatile products of the coal being driven off 
leaving a substance of variable qualities depending on the 
nature of the coal used and the mode of coking. It may 
be porous and light or dense and compact; soft and ten- 
der or hard and resisting; varying in color from black 
to gray; its luster sometimes dull, at others, of metallic 
brightness. It is less inflammable and less combustible 
than charcoal, but yields a higher temperature on burn- 
ing. Professor Richardson observes: "The best coke 
for furnace use is that used by brassfounders, and has a 
steel-gray color, with a somewhat metallic luster." 

Coke does not easily ignite, and usually requires a 
little admixture of charcoal to kindle it; a strong draught 
is also necessary to burn it. It has been much used in 
continuous-gum work and analogous operations. 

Petroleum. — Kerosene or coal oil is one of the prod- 
ucts in distilling crude petroleum, and is much used 
where gas is not available. Since most dental lamps and 
stoves are of metallic construction, due precaution must 
be exercised to use only good " high test" oil, i. e., that 
which has been properly freed from the volatile products 



MELTING METALS. 59 

of petroleum and is capable of withstanding the maxi- 
mum temperature developed by the lamp-flame without 
evolving dangerously combustible gases. It has been 
found that 5 per cent, of crude naphtha reduces the flash- 
ing-point from 118° to 70° F. 

Gasoline. — A colorless, volatile, inflammable liquid; 
one of the products of the distillation of crude petroleum, 
having a specific gravity of . 629 to .667 at 60° F. It is so 
volatile that if a current of air be passed through it at 
ordinary temperatures a highly dangerous combustible 
gas is formed by the mixture of gasoline vapor and 
atmospheric air. It is much used as a fuel in vapor 
stoves and for carburizing air-gases, etc., see Figs. 8 
and 19. 

Coal Gas. — Illuminating gas as it is frequently 
called is a distillatory product of the varieties of coal 
known as bituminous and cannel. 

EXPERIMENT No. 7.— Fill the bowl of an ordinary clay pipe with 
small fragments of bituminous coal, lute over with clay and place in a 
bright fire; immediately smoke is seen to issue from the stem which pro- 
jects beyond the fire. The smoke soon ceases, and if a lighted taper is then 
applied to the orifice of the stem, the issuing gas burns with a bright 
steady flame, while a proportion of a black, thin, tarry liquid oozes out 
from the stem. After the combustion ceases there is left in the bowl of the 
pipe a quantity of char or coak. 

This simple experiment is, on a small scale, an exact 
counterpart of the process by which the destructive dis- 
tillation of coal is accomplished in the manufacture of 
gas. The products of this distillatory process are classed 
in the gas works as gas, tar, ammoniacal liquor and 
coak. The gas is purified by removing the tar and 
ammoniacal liquor, and then passed into the pipes 
for consumption. It is composed of a variety of sub- 
stances divided into two classes, viz.: ist — Non-lumi- 
nous supporters of combustion, embracing hydrogen 
(H), marsh gas (CH 4 a lightly carburetted hydrogen), 



60 PRACTICAL DKNTAI, METALLURGY. 

and carbon monoxide (CO); 2d — The lumzniferous con- 
slituents, which include the hydrocarbon gases acet- 
ylene (C 2 H 2 ), olefiant gas (C 2 H 4 , a heavy carburetted 
hydrogen), propylene (C 3 H 6 ), butylene (C 4 H 8 ), and most 
important of all the vapors of the benzol (C 6 H 6 ), and 
naphtbalin (C IO H 8 ) series. 

As a source of light and heat gas is most extensively 
used in dental laboratories. See gas furnaces. 

REDUCTION OF ORES.— Occasionally metallic ores 
are obtained in compact masses of comparatively pure 
metal, from which the accompanying matrix or gangue 
can be detached by the hand or hammer. But such in- 
stances are rare. In most cases the ore comprises 
but a small percentage of the gangue. Hence it is expe- 
dient to purify it as much as possible before attempting 
to liberate the metal. This is accomplished generally 
by crushing and washing out the earthy matter as far as 
practicable. The ore is then subjected to roasting, 
amalgamating, or dissolving operations for the reduction 
or liberation of the metal. 

The great majority of metals are reduced by heat. In 
this process the ore, along with some kind of flux, is 
exposed to the direct action of a powerful fire, which in 
most cases has a chemical as well as a physical function. 
It is intended, with the assistance of the flux, to break 
up or burn away some chemical compound or component, 
or it is meant to deoxidize the ore. 

For these firey operations immense furnaces are con- 
structed of brick, granite, or other building stone, and 
lined with refractory or fire-resisting clay, brick, etc. 

FURNACES are best classified, by the method 
adopted for supplying air, into two classes, viz., (1) 
blast-furnaces, (2) chimney-draught furnaces, the latter are 
also known as air and wind furnaces. 



MELTING METALS. 



61 



Blast-Furnaces are supplied with air from a source 
under pressure (B f Fig. 2) sufficient to overcome the 
resistance to its free passage presented by the packed 




Fig. 2. Sectional View of Blast-Furnace. 

columns of fuel, flux, and ore. These are the oldest and 
simplest forms of metallurgical contrivance. The open- 



62 



PRACTICAL DENTAL METALLURGY. 





hearth blacksmith's forge is a simple 
type of the same principles involved in 
the completely closed-in blast-furnaces 
of gigantic dimensions* in use for work- 
ing and producing the various com- 
pounds of iron. 
Fig. 2 is a ver- 
tical section of a 
blast-furnace. 
The upper cone 
D Cis known as 
the stack proper, 
the lower one 
Fig. 3. Reverberatory Furnace. from the broad- 

est part C to the tuyeres B, as the boshes, and the lower 
cylindrical part A, B, as the hearth. 
A Chimney Draught, Air, or Wind 
Furnace is supplied with air drawn 
through it by a partial vacuum in the 
chimney formed by the heated gases 
on their way to the atmosphere. The 
reverberatory furnace is a type of this 
class. Fig. 3 represents a vertical sec- 
tion of the reverberatory furnace. 

The characteristic point in this furnace 
is, that the fire-chamber A is separate 
from the one in which the material to 
be operated upon is placed — the heat 
and flame passing over the charge, as 
from A, D, E. B is a low wall divid- 
ing the fireplace from the working bed 
C, and is known as the fire-bridge. At the opposite end 




Fig. 4* 
Crucible Furnace. 



* In the Middlesborough district, England, is a furnace 103% feet in height, 
and of 33,000 cubic feet capacity. 



MELTING METALS. 



63 



there is sometimes a second bridge of less height called 
the flue-bridge, E. The ore is introduced from hoppers 
at H, the slag is withdrawn at A", and the metal run out 
by a tap-hole at L. 

For melting gold and silver, as for all ordinary melt- 
ing operations, Mr. Makins recommends one after the 
styleof Fig. 4, which 
should form a part of 
the fitting of all 
metallurgical labora- 
tories. This may be 
built in an ordinary 
house-flue with a 
chimney about thirty 
times the diameter of 
the fit r 71 a c e — o r 
thirty feet in height, 
for a furnace of one 
foot in diameter. 

A third class of 
furnaces is known as 
Muffle- Furnaces, and 
under this head are 
to be found the assay- 
er's furnace and the 
contimwus-gum fur- 
nace, Fig. 5. The 
principle is to avoid 
contact with either 
fuel or flame, and in 
the case of continu- 
ous-gum work even the products of combustion are care- 
fully excluded. 

Dental Laboratory Furnaces. — For melting metals 




FrG. 5. Continuous-Gum Furnace. 



64 PRACTICAL DENTAL METALLURGY. 

in the dental laboratory, the small, compact, blast-furnace 
devised by Mr. Fletcher, and shown in Fig. 6, is the 
simplest and most convenient. 

It consists of a cylindrical casing and perforated cover 
made of fire-clay which has been mixed with three or 



?>£Slfc.UV<..^.>U=i. 

Fig. 6. 



four parts by bulk of sawdust and burned. Through a 
hole near the bottom of the casing the mixed air and gas 
is injected, the latter being regulated by a check near 
the mixing chamber. The gas is received from as large 
a supply-pipe as convenient, and the air driven in by 



Fig. 7. 

means of the foot-bellows. The crucibles used should 
not exceed 2 by 2% inches. According to Mr. Fletcher, 
" With half-inch gas-pipe and the smallest foot-bellows 
the smallest sized furnace will melt a crucible of cast 
iron in seven minutes, tool steel in twelve minutes, and 



MELTING METALS. 



65 



nickel in twenty-two minutes, starting with all cold." 
Gold, silver, or copper may be readily fused in one of 
these furnaces where gas is accessible. Where gas is 
not convenient, the 
metals or dental- 
amalgam alloys may 
be melted very satis- 
factorily in a near-by 
blacksmith's forge, 
or in a coke or coal 
fire in an ordinary 
stove or open fire- 
place if the draught 
is sufficiently strong. 
If the draught is 
weak the combus- 
tion of the fuel may 
be better accom- 
plished by improvis- 
ing a blast by pass- 
ing a small piece of 
gaspipe between the 
grate-bars of the fire- 
place or stove and 
attaching to this the 
hose from the foot- 
bello ws . In this 
manner a consider- 
able quantity of gold, 
silver, copper, or 
alloy may be melted FlG 8 

with little trouble. 

A modified type of Fig. 6 has been devised (Fig. 7) 
retaining all its peculiar advantages, but burning petro- 




66 



PRACTICAL DENTAL METALLURGY. 



leum, instead of gas, as fuel. The burner dispenses with 
a wick, by being constructed on the principle of an 
atomizer. It is supplied with a device for regulating the 
supply of oil, which is operated by the milled nut at A, 
and for the supply of an annular jet of air which is regu- 
lated by turning the sleeve B. 

The construction is such that it may be taken apart 
and cleaned, in case of any obstruction. The furnace 
stands are interchangeable for either gas or petroleum. 
Where illuminating gas is not attainable a much more 
convenient form of furnace than that shown in Fig. 7 may 
be had as illustrated in Fig. 8. The gasoline generator 
placed beneath the bench is attached to foot-bellows and 
furnace. 

The small crucible gas-furnace without blast, illus- 
trated by Fig. 9 will be found most convenient for 

melting the more infusible 
metals of the dental labora- 
tory. It will receive a crucible 
not to exceed 2% by 2^ 
inches, and when supplied 
with a 6-foot chimney, will 
melt copper, gold, silver, etc., 
in a very few minutes, or cast 
iron in 30 minutes, all started 
cold. The furnace is so con- 
structed that the gas enters 
a chamber at the bottom of the 
burner through a device similar 
to a Bunsen burner, mixing 
with air as it enters, and burned at the upper ends of a 
series of concentric tubes, furnishing air spaces alternately 
with those supplying the mixture of gas and air. The 
whole burner is constructed of iron, and will be found 




Fig. 9. 



MELTING METALS. 



67 



better able to withstand an intense heat, more durable 
and quicker in its operations than the old pattern, with 
gun-metal tubes. In case metal should be spilled into the 
burner, it can be easily taken apart for its removal. 

Downie's crucible furnace, Fig. 10, is especially de- 
signed for melting metals, such as gold and silver, 
making dental-amalgam alloys, experimental work, etc. 




Fig. 10. 

It is also very useful for brazing, soldering, heating up 
bridge-cases or metal plates to solder, etc. It has two 
removable rings of different widths, which set on above 
the flaring base to carry the heat up around the crucible, 
the wide or narrow ring being used, according to the size 



68 



PRACTICAL DKNTAL METALLURGY. 



of the crucible; or both rings may be put on at the same 
time. It also has a conical-shaped top which can be set 
on above the rings to confine the heat when it is desired 
to fuse any high fusing substance. 

This furnace can be used for baking continuous-gum 
work, or any other porcelain work. 




Fig. 11. 

For those metals which fuse much before redness, 
such as zinc, lead, tin, and their alloys, iron ladles are 
usually employed. In the dental laboratory for melting 
zinc, lead, or alloys, for making dies and counter-dies, 

iron melting-pots (Fig. 11), 
capable of holding from 6 to 
10 pounds of metal, are used. 
The metal may be most con- 
veniently melted over one of 
Fletcher's solid-flame gauze- 
top stoves, shown in Fig. 
12. The stove is so con- 
structed that the gas mixed 
with the proper proportion of air from below is burned 
above the gauze top, yielding a blue flame, intensely 
hot and perfectly solid and uniform. The consumption 
of gas is about two cubic feet per hour for each square 
inch of gauze surface. It will melt an ordinary pot of 
lead in 12 minutes, depending on the gas supply. An 




MELTING METALS. 



69 



apparatus in which gasoline may be 
used, when gas is not available 
(much used by plumbers for melting p IG# 13 
solder), is recommended by Dr. 
Kirk* for melting zinc and lead in the 
dental laboratory. In the absence of gas 
supply it is probably more convenient to 
melt these metals in the open fireplace or 
in the stove. 

BLOW-PIPES.— For minor melting 
operations, such as melting small quantities 
of gold, silver, or copper, or in soldering, 
the blow-pipe in some of its variously modi- 
fied forms is usually employed. These in- 
struments are classified as simple and com- 
pound. 

A simple blow-pipe of plainest pattern is 
shown in Fig. 13, A. It consists of a tube 
of brass or other metal tapering gradu- 
ally from the larger end, which is inserted 
in the mouth, to the other extremity, 
which is curved and mounted with a cone- 
shaped tip to protect it from the action of 
the flame; the caliber of the instrument 
terminates here in a very small orifice. The 
point of the instrument is frequently tipped 
with a more refractory metal, such as plati- 
num, and the end to be received in the 
mouth is sometimes plated with a less oxi- 
dizable metal, such as silver. The whole is 
usually from twelve to fourteen inches in 
length, and the large extremity from one- 
half to three- fourths of an inch in diameter. 

* American System of Dentistry, Vol. Ill, p. 816. 



70 



PRACTICAL DENTAL METALLURGY. 



As more or less moisture accumulates in the tube from 
the mouth, a second form has been devised (Fig. 13, B), 
to the stem of which, nearer its smaller extremity, is 
adjusted either a spherical or cylindrical chamber, which 
collects and retains the moisture as it forms within the 
pipe. The moisture is prevented from flowing into the 




Fig. 14. 

smaller end of the tube beyond by the projection of that 
portion of the stem a slight distance into the chamber. 

Fletcher has much improved upon this simple form of 
blow-pipe by coiling the smaller extremity of the stem 
into a light spiral over the point of the jet (Fig. 14). 
The air as it traverses the coil is heated, producing a 
hot blast instead of a cold one, as in the old form. Such 
an instrument enables the operator to produce a higher 
temperature than that produced with the ordinary pipe 
with the same amount of energy. The same pipe may 




Fig. 15. 

be fitted with a hard-rubber mouth-piece, which is less 
tiresome to grip in the mouth. 

Another form by the same inventor is illustrated in 
Fig. 15. This is wholly unlike any mouth blow-pipe 
yet devised, and admits of considerable latitude of 



MELTING METALS. 



71 



movements in the application of heat by the rubber tubing 
connected with it. The mouth-piece is so constructed that 
a shield protects the lips in such a manner that long-con- 
tinued blowing may be practiced without undue strain on 
the lip?, while the opening is well under the control 
of the tongue. It is also provided with a condensing 
chamber and interchangeable tip, either plain or coiled. 

FLAME. — Flame consists of a sheet of burning gas. 
The burning candle presents a type of all other flames, 
serving to illustrate its general structure. If such a 
flame be examined closely it will be found 
divisible into four separate parts. The por- 
tion which immediately surrounds the wick, 
represented in the figure by A, B, is a deep 
blue. This portion becomes thinner as it 
ascends, until it gradually disappears. It 
owes its color to the combustion of carbon 
monoxide, and is the coolest portion of the 
flame. The center (C) of the flame is dark, 
i. e., non-luminous, and consists of the 
gases produced by the decomposition of the 
fat, and is, in the flame we are considering, FlG - 16, 
highly charged with carbon. These gases do not come 
in contact, at this point, with sufficient oxygen to burn 
them, and therefore remain unchanged. 

Surrounding the dark cone-shaped center is the bril- 
liant yellowish- white flame D. Here the gases are 
enabled to combine with the oxygen of the air. The 
hydrogen burns, and the intense heat generated by its 
combustion ignites the minute paiticles of carbon which 
are held in suspension by the ascending gas, rendering 
them highly incandescent; hence the luminosity. 

All the gas, however, is not burned in the central cone 
of flame. A portion of it escapes beyond and burns more 




72 PRACTICAL DENTAL METALLURGY. 

slowly, in consequence of its being mixed with steam, 
carbon dioxide, and other products of combustion, to- 
gether with a little unburnt carbon. This forms the 
outer dimly luminous envelope E. The greatest heat is 
found in the external ring EE, for here the air has free 
access to the exterior. The heat, however, decreases 
from Eto E t and from Eto A, B. 

The Use of the Blow-pipe consists in injecting a 
stream of atmospheric oxygen into this inner cone of 
gas, so as to cause the free combustion of it and the 
luminous particles of carbon evolved from it; while at the 
same time the operator directs the flame over the object 
to be heated. 

The Flame of the Blow-pipe consists of three parts 

(Fig. 17). A, an inner 





A "1"> B ^><D> cone of unburned 

gases mixed with 
Fig. 17. oxygen (air) from the 

blow-pipe; a second, B, blue, pointed, and well defined; 
and a third, C, yellowish, and somewhat vague. 

The Reducing Flame (R. F.). — Just beyond the tip 
of the inner blue cone is the reducing flame, so called 
from the fact that if a metallic oxide be immersed in it 
the oxygen of the metal will be abstracted by the heated 
carbon from the hydrocarbon gas, to form carbon diox- 
ide, and the metal liberated. At the same time the metal 
is protected from reoxidation by being thoroughly cov- 
ered with the flame. To produce this flame the jet of 
the pipe should be fine, and placed a little above and to 
the side of the flame. 

The Oxidizing Flame (O. F.). — Just beyond the tip 
of the less distinct cone C is the position where, if a 
metallic bead be exposed, it will combine with the oxy- 
gen of the air, becoming an oxide. The object is to 



MELTING METALS. 



73 



heat the metal hot enough to favor a rapid chemical com- 
bination with the oxygen of the air, at the same time to 
draw as large a quantity of external air to the point as 
possible; hence, the bead of metal is not only imme- 
diately melted, but is oxidized by the external air; 
therefore the farther it can be kept from the tip and 
sufficient heat be maintained, the more perfect will be 
the oxidation. This flame is formed by placing the jet, 
which should have a tolerably wide opening, imme- 
diately over the wick or burner, and injecting the air 
into the flame. The cone then loses its yellow color and 
becomes an intensely hot, long, narrow, blue flame. 

Reduction on Charcoal. — Reduction is much more 
easily effected by the employment of a block of charcoal 
as a support. It not only assists in heating the bead of 
metal by becoming hot, but it also assists in the reducing 
action by combining with the oxygen of the oxide, form- 
ing carbon dioxide, and liberates the metal. 

LAMPS. — Flames for soldering may be derived from 
oily spirit, or gas lamps. 

Oil Lamps. — The fluid hydrocarbon, petroleum, or 
coal-oil is very inexpensive, and where gas is not avail- 
able is much used. Fig. 18 rep- 
resents a soldering lamp. An oil- 
lamp to be satisfactory should 
hold about one to two pints and 
should have a tapering spout from 
three to five inches in length. 
The spout should be well filled 
with wick, but not too tightly, for 
fear of preventing free saturation Fig. 18. 




74 



PRACTICAL DENTAL METALLURGY. 



with the oil. Proper care should be exercised to guard 
against all accidents occasioned by ill-fitting parts, filling 
and adj usting. With a good lamp, an entire artificial den- 
ture can be sol- 
dered, or one or 
two ounces of 
gold melted. 
Pure sweet oil 
or lard oil may 
also be used in 
these lamps for 
soldering. 

Fig. 19 illus- 
trates a com- 
pound blow-pipe 
(D) used with 
gasoline gas. 
It is provided 
with a geiiera- 
tjr(^) and bel- 
lows (B) with 
which it is con- 
nected^) simi- 
larly to that in 
Fig. 8. 

Spirit Lamps. 
— Much the 
same lamps, as 
illustrated in 
Fig. 18, may be 
used for alco- 
hol, which is much preferable to coal-oil on account of 
its cleanliness and the less liability to accident. With a 
lamp similar to the one represented in Fig. 20, the 




Fig. 19. 



MELTING METALS. 



75 




spirit is entirely uninfluenced by the heat of the flame, 

and explosion is rendered almost impossible. 

In Fig. 21 is represented a self-acting lamp and blow- 
pipe. The lamp reservoir and 
the boiler will each hold about 
a half-pint of alcohol. Light- 
ing the flame under the boiler 
vaporizes the alcohol in it 
rapidly, the pressure forcing 
the vapor through the pipe 
into the large flame at the side 
Fig. 20. of the lamp, forming a very 

practicable and efficient blow-pipe. The force of the blast 

is regulated by raising or 

lowering the boiler; the 

spread of the flame by 

using the larger or 

smaller nozzle. The ap- 
pliance is substantially 

made of spun brass, and 

the boiler is provided 

with a safety-valve. A 

set-screw on the upright 

permits the boiler to be 

raised or lowered or 

swung to one side. One 

of the nozzles is carried 

on the top of the safety-valve; the other in position on 

the pipe. 

Gas Lamps. — The gas may be most effectively used 
by an apparatus on the principle of the one illustrated 
in Fig. 22, which consists of a sort of duplex Bunsen 
burner. 




76 



PRACTICAL DENTAL METALLURGY. 



Compound Blow-pipes. — The difficulty in maintain- 
ing a flame of uniform size and intensity, owing to the 
fact that the blow -pipe and lamps are separate, the lack 

of latitude allowed the op- 
erator by the fixed position 
of the blow-pipe, and the 
introduction of gas in the 
experimental laboratory led 
to a form known as the com- 
pound blow-pipe, Fig. 19. 
This instrument is so con- 
structed that it virtually 
consists of a lamp and blow- 
pipe all in one. In general 
it consists of two metallic 





Fig. 22. 
concentric tubes, one a smaller, terminating in a fine jet 
and placed within the first, so that the finer jet is accu- 
rately centered in the orifice of the larger tube, Fig. 23. 
Gas is supplied to the larger tube by an offset tube on 
the side of the nearer end, and flowing through the space 
in the large tube on all sides of the enclosed smaller 
tube to the opposite end, where it is ignited. Air from 
the lungs or other source is transmitted through the 



MEI/TING METALS. 



77 



inner tube to the center of the flame. The supply of 
both gas and air may be regulated in most of the later 




Fig. 23. 



patterns by checks within reach of the fingers of the 
same hand holding the instrument. The blast from the 




A n n 7 

mouth is most convenient for small heating, but when 
high temperatures are desired for some time, one of the 



78 



PRACTICAL DENTAL METALLURGY. 



various forms of mechanical blowers is necessary. A 
mechanical blower devised by Dr. Burgess is illustrated 

in Fig. 24. It consists of a 
cylindrical metallic reservoir 
connected beneath with a 
pump cylinder, worked by 
means of a heel-and-toe 
treadle. The air is forced 
into the reservoir through a 
valve, and escapes through a 
small opening on the side 
near the top to a flexible rub- 
ber hose which conveys it to 
the blow-pipe. A far more 
satisfactory apparatus is 
found in the foot-bellows de- 
vised by Mr. Fletcher and 
shown in Fig. 25. 

SUPPORTS.— When sol- 
dering or melting gold or 
silver with the blow-pipe 
flame, it is necessaryjto place the articles to be soldered, 
or the metals to be melted, upon some sort of a support. 




Such supports may 
be improvised of 
blocks of charcoal, 
if the temperature 
is not to be too 
high, or large 
blocks of pumice- 
stone encased in 
plaster, giving the 
whole a variety of 
forms. One, de- 




Fig. 25. 



MELTING METALS. 



79 



signed by Professor C. L- Goddard which the author 
uses very comfortably, was made by making a mold of a 
hemisphere from a smooth croquet-ball, by pouring 
some plaster of pans into a pasteboard box about five 
inches square, and then dipping the ball, and removing 
it when the plaster had hardened. The mold thus made 
was then varnished and filled with soft plaster, on the 
top of which was imbedded a large piece of pumice- 
stone. When this hardened, the hemisphere was sepa- 
rated from the concavity, and the block containing the 
latter cut down until it covered but little over half of the 
hemisphere, when it was reinserted. The whole was 
then varnished, and presented a very compact, con- 
venient soldering-block, fitted in a socket which permits 
it to be poised at almost any angle. 

Blocks of charcoal may also be covered on all sides 
but one with about one-half inch thickness of plaster. 
They then furnish 
clean and convenient 
supports for small sol- 
derings and meltings. , 

Fig. 26 forms a 
convenient asbestos | 
soldering-block, and j 
Fig. 27 represents ■ 
another more easily p 
handled. The block 
is of carbon and is fur- 
nished with a wooden 
handle. Fig. 28 represents a circular asbestos soldering- 
block or -tray, with raised rim, set in a brass box, mounted 
on a wooden handle. The four holes are for the reception 
of brass pins, to hold the work in place. The investing 
material is made of a prepared asbestos fiber. This 




Fig. 26. 



80 



PRACTICAL DENTAL METALLURGY. 



material is simply dampened. When the objects to be 
soldered consist in part of artificial teeth, such as a denture 




Fig. 27. 
or bridge, a support of the style of Fig. 29, a small hand- 
furnace or soldering-pan, is very satisfactory. It consists 





Fig. 28. Fig. 29. 

of a funnel-shaped receptacle made of sheet iron, with a 
light grate or perforated plate of the same material adjusted 



MEETING METALS- 



81 



near the bottom, and an opening on one side, underneath 
the grate, for the admission of air. The upper part of 
the holder is surrounded by a cone-shaped top, which 
may be readily removed by a handle attached to it; while 
to the bottom of the furnace is attached an iron rod, 5 




Fig. 30. 



or 6 inches in length, enclosed in a wooden handle at its 
unattached end; when the case is sufficiently heated, the 
top may be lifted off, and the case remaining in the fur- 
nace soldered with the blow-pipe in the usual manner, 
the furnace then serving the place of a support. 

INGOT MOLDS are usually made of iron in various 
forms to suit the requirements, those for the noble 




Fig. 31. 
metals generally having the form shown in Fig. 30, 
which is so constructed that the side next to the handle, 
which also acts as a set-screw, can be moved laterally 
upon the opposite side, so that the intervening slot may 
be made narrow or wide. Ingots are also frequently cast 



82 



PRACTICAL DENTAL METALLURGY. 




into molds of sandstone, charcoal, compressed carbon, 
pumice-stone, or asbestos preparations. Fig. 31 repre- 
sents such an apparatus suitable as a support for melt- 
ing, and as an ingot mold for the molten metal by merely- 
tipping the slab and placing a cold, flat 
surface over the still heated metal in the 
mold. 

Fig. 32 is an arrangement for melt- 
ing and molding noble metals without 
the use of a furnace. Referring to the 
engraving: A is a crucible of molded 
carbon supported in position by an iron side-plate. C 
the ingot mold. D a clamp holding the crucible and 
ingot mold in position, and swiveling on the cast iron 
stand B. The metal to be melted is placed in the cruci- 
ble A, and the flame of a blow-pipe is directed on it until 
it is perfectly fused. The waste heat serves to make 
the ingot mold hot, and the whole is tilted over by 
means of the upright handle at the back of the mold. 
A sound ingot may be obtained at any time in about 



Fig. 32. 



two minutes. 



CHAPTER V. 
ALLOYS. 

AN ALLOY is the compound or mixture of two 
or more metals effected by fusion. 

AN AMALGAM is an alloy of two or more metals, 
one of which is mercury. 

Few metals are employed in the pure state, with the 
exception of iron, copper, lead, tin, zinc, platinum, alum- 
inum; they are more frequently used in the form of alloys 
for technical purposes. Every industrial application 
necessitates special qualities that may not occur in any 
isolated metal, but which may be produced by the proper 
mixture of two or more of these. For example: silver 
and gold are much too soft and pliable for plate, coin or 
jewelry, but by the addition of certain amounts of cop- 
per they are rendered harder and more elastic, while 
their color and other valuable qualities are not impaired. 

Copper is also too soft and tough to be wrought in a 
lathe, but when alloyed with equal parts of zinc it forms a 
hard, beautiful, yellow-colored alloy known as brass, of 
great usefulness, and more easily worked than the 
pure metal. 

Alloys are equally interesting, from a scientific stand- 
point, for they may be regarded not only as mere mix- 
tures of metals, but in many instances as true chemical 
compounds. Matthiessen* regarded it as probable that 
the condition of an alloy of two metals in a melted state 
may be either that of : 1. — a solution of one metal in 
another; 2. — a chemical combiiiation; 3. — a mechanical mix- 
ture; or, 4. — a solution or mixture of two or all of the above; 
and that similar differences may exist as to its condition 
in the solid state, defining a solid solution as " a perfectly 
homogeneous diffusion of one body in another." 

* British Association Reports, 1863, p. 97. 



84 PRACTICAL DENTAL METALLURGY. 

1. A Solution of One Metal in Another. — Some 
metals when melted together will apparently unite in the 
same manner that water mixes with alcohol, in all pro- 
portions and indefinitely, forming a perfect homogeneous 
mass and exhibiting no tendency to separate on cooling. 
The mixture thus formed will, as regards chemical and 
physical properties, be a mean of the two components; 
that is to say, it will partake of the properties of both, 
those of the one predominating just as one or the other 
may be in excess. Lead and tin form such an alloy. 

2. A Chemical Combination. — Other metals when 
melted together do, without doubt, form true chemical 
compounds. In the phenomena which accompany such 
union, and in the properties of the resulting products, we 
observe that which characterizes the manifestation of 
affinity, that is, an evolution of heat and light, resulting in 
the formation of substances having a definite composition, 
distinct crystalline form, and a variety of properties differ- 
ent from those of the constituents. Thus, if a piece of 
clean sodium be rubbed in a mortar with a quantity of dry 
mercury, the sodium combines with a hissing sound, and 
a considerable increase of mass temperature is noticeable 
on the addition of each successive piece of sodium. 

EXPERIMENT No. 8.— Throw a small piece of clean, dry sodium, 
upon the surface a small amount of clean, dry, and warmed mercury; a 
chemical union takes place immmediately, accompanied by heat and incan~ 
descence, forming crystalline amalgam. 

When the mass cools, long needles of a white, brilliant 
alloy of definite composition crystallizes from the middle 
of the liquid, and the excess of mercury may be sepa- 
rated by decantation. Platinum, iridium, gold, and 
silver unite with tin, accompanied by an evolution of 
heat. If the tin is in excess, upon cooling, the mass 
very much resembles that metal, but if the ingot be 
treated with strong hydrochloric acid, the excess of tin is 
dissolved, and crystals of a definite alloy of tin and the 



ALLOYS. 85 

precious metals remain.* Examples of such union by 
definite proportion often occur in nature, as, for instance, 
we have the native alloys of gold and silver, in which 
four, five, six, or twelve atoms of gold are found com- 
bined with one of silver. Several other metals? such as 
iridium and osmium, as iridosmine, palladium, and plati- 
num and others occur as native alloys. 

3. A Mechanical Mixture. — It must be admitted 
that, in the case of mixing substances, or of dissolving 
one in another, the result is much dependent upon the 
affinity — or compatibility — existing between them. Thus 
we may attempt to dissolve camphor in water, but here 
the affinity is so feeble that an exceedingly small propor- 
tion will be dissolved; while, on the other hand, if we 
employ alcohol instead of water, a large quantity of the 
solid camphor may be taken into solution. Then, if 
water be subsequently added to such a solution, the 
spirit, having a greater affinity for the water than for the 
camphor, will leave the latter, to be separated again and 
assume a solid form. Thus, silver or gold will not unite 
with iron, nor zinc to any great extent with lead. Other 
metals melted together which possess little or no affinity 
for each other, do not readily unite, but remain separate 
and distinct; alloys of lead and copper, "pot-metal 
alloys," show on their fracture surfaces, when viewed 
under a strong glass, a network of copper and a small 
amount of lead, enclosing irregularly globular masses of 
nearly pure lead in its meshes. Such alloys are subject 
to liquation, or separation, by heat — the lead separating 
out, leaving the copper in a porous mass. 

4. A Solution or Mixture of Two or All of the 
Above. — It is obvious that most alloys may be correctly 
classed under this head, when we consider the almost 
infinite proportions in which metals are combined. 

* See chapter on Tin. 



86 



PRACTICAL DENTAL METALLURGY. 



THE PHYSICAL PROPERTIES OF ALLOYS 

cannot be anticipated, and are only determinable by 
actual experiment. Very minute proportions of some 
metals added to others will produce an alloy with 
properties foreign to either of the constituents. Thus, a 
small quantity of lead fused with gold will produce a 
brittle alloy, though each metal is malleable. 

Specific Gravity. — If this property be calculated from 
that of the components — assuming that there is no con- 
densation of volume — the resulting number may be 
greater than, equal to, or less than, the experimental 
result. Thus, the alloys of silver and gold have a less spe- 
cific gravity than the theoretical mean of the components; 
whereas copper and zinc vary in the opposite direction. 

The following table,* by Th^nard, shows examples of 
this variation : 



Alloys Possessing a Greater Specific 

Gravity than the Mean of Their 

Components. 



Alloys Having a Specific Gravity 

Inferior to the Mean of Their 

Components. 



Gold 


and 


Zinc 


Gold 


and 


Silver 


< i 


>i 


Tin 


< i 


i < 


Iron 


< i 


i< 


Bismuth 


it 


<< 


Lead 


■ < 


< < 


Antimony 


<< 


<( 


Copper 


(i 


(< 


Cobalt 


<< 


<( 


Iridium 


Silver 


(i 


Zinc 


« < 


<. 


Nickel 


it 


< c 


Lead 


Silver 


<< 


Copper 


«( 


<< 


Tin 


Copper 


<< 


Lead 


< i 


<< 


Bismuth 


Iron 


« < 


Bismuth 


(< 


< < 


Antimony 


< t 


< < 


Antimony 


Copper 


«( 


Zinc 


<( 


<< 


Lead 


1 1 


<< 


Tin 


Tin 


« < 


Lead 


i < 


cc 


Palladium 


< < 


< c 


Palladium 


tc 


< < 


Bismuth 


< < 


a 


Antimony 


<( 


<< 


Antimony 


Nickel 


«> 


Arsenic 


Lead 


( « 


Bismuth 


Zinc 


<< 


Antimony 


u 


1 ( 


Antimony 








Platinum 


(I 


Molybdenum 








Palladium" 


Bismuth 









* Phillip's Metallurgy. 



ALLOYS. 87 

It is common among authorities who publish determi- 
nations upon specific gravities of the alloys to give the 
calculated as well as the observed specific gravity. 

The Color of an alloy is usually resembling or par- 
taking of that metal which predominates. Some few 
exceptions are quite notable, for instance gold 2 to 6, and 
silver 1 part produces an alloy of a greenish color, and 
it is said that % 4 of silver is sufficient to modify the cclor 
of gold. Nickel and copper form alloys varying from 
copper-red to the bluish-white of nickel. With a content 
of 30 per cent, of nickel the alloy is silver white ; while 
with zinc, copper yields a variety of shades, from the 
silver white of copper 43, and zinc 57 parts, to that of 
red brass, which contains 80 per cent, or more of copper. 

Malleability, Ductility, and Tenacity. — These prop- 
erties are generally very much modified by alloying. As 
a rule the malleability and ductility are decreased, even 
when two malleable and ductile metals, such as gold and 
lead, are alloyed together — a very small content of lead 
destroying the malleability and ductility of the noble 
metal. Again, copper 94 and tin 6 parts form an ex- 
ceedingly brittle alloy. Generally the ductility decreases, 
while the hardness as compared with that of the con- 
stituent metals increases to a considerable extent; for 
example, gold and platinum, two very ductile and soft 
metals, afford an alloy much harder and of greater elas- 
ticity than either. Gold and silver, being too soft for 
currency, are alloyed with 10 per cent, of copper, which 
gives them the required hardness. A few metals, anti- 
mony, for instance, possess the property of making 
metals harder. Mr. Makins states that l-1900th part of 
this brittle metal will make gold quite unworkable. As 
a rule, a brittle and a ductile metal afford a brittle alloy; 
yet copper and zinc yield a malleable and ductile brass. 



88 PRACTICAL DENTAL METALLURGY. 

The tenacity is generally very much increased , as is 
shown by the following results of Matthiessen's experi- 
ments. Wires of the same gauge were employed, and 
the weights causing their rupture before and after alloy- 
ing noted as follows: 

Lbs. at Rupture. 

Copper, unalloyed 25 to 30 

Tin, " , under 7 

Lead, " " 7 

Gold, " 20 to 25 

Silver, " 45 to 50 

Platinum, " , 45 to 50 

Iron, " 80 to 90 

Lbs. at Rupture. 

Copper, alloyed with 12 per cent. Tin 80 to 90 

Tin, •' " " " Copper 7 

Lead, " " Tin 7 

Gold, " " Copper 70 

Silver, <; " Platinum 75 to 80 

Steel (iron compounded with carbon) . above 200 

Fusibility. — The fusing point of an alloy is always 
lower than the least fusible metal entering into its com- 
position, and is sometimes lower than that of any of the 
components. Thus an alloy composed of 10 parts lead 
and 4 parts tin fuses at 470° F., melting lower than the 
less fusible lead (617° F.), but at a greater temperature 
than tin (442° F.); and an alloy composed of 4 parts lead, 2 
parts tin, 5 to 8 parts bismuth, and 1 to 2 parts cadmium 
(Wood's metal) melts at 140° to 161° F., lower than 
that of any of its constituents — tin being the most fusi- 
ble (442° F.). Alloys of lead and silver, containing a 
small quantity of the latter, are more fusible than lead, 
and sodium and potassium form a fluid alloy at ordinary 
temperatures. 

Matthiessen* explains why the fusing point of alloys 
is uniformly lower than the mean of those of their con- 
stituents: "It is generally admitted that matter in the 

* Makins' Metallurgy, p. 65. 



ALLOYS. 89 

solid state exhibits excess of attraction over repulsion, 
whilst in the liquid state these forces are balanced, and 
in the gaseous state repulsion predominates over attrac- 
tion. Let us assume that similar particles of matter 
attract each other more powerfully than dissimilar ones 
attract each other. It will then follow that the attrac- 
tion subsisting between the particles of a mixture will be 
sooner overcome by repulsion than will the attraction in 
the case of a homogeneous body; hence, mixtures should 
fuse more readily than their constituents." 

Sonorousness. — This property is most wonderfully 
developed in some instances. Copper and tin, two 
metals which possess the quality in but a small degree 
comparatively, unite to form an alloy known as "bell 
metal," the normal composition of which is, copper 72 or 
85, and tin 15 or 26. Copper and aluminum also yield 
alloys of remarkable sonorousness. 

Conductivity. — The property of conductivity, either 
for electricity or heat, in an alloy is much inferior to 
that of the pure metals. Advantage is taken of the high 
electrical resistance in some of the alloys, such as Ger- 
man silver, for measuring the resistance of long lines of 
telegraph wire, the electromotive force or working power 
of batteries, for making rheostats and other apparatus 
for controlling the electric current, etc. 

Decomposition. — Heat decomposes alloys containing 
volatile metals like mercury or zinc. It requires a tem- 
perature much above the boiling point of the metal, 
however, to completely separate all traces of it from an 
alloy, and in most instances this cannot be accomplished 
even then without the assistance of chemical agency. 
When gold is contaminated with tin, the latter cannot be 
removed entirely by roasting; but if heated with small 
quantities of potassium nitrate, which serves to oxidize 



90 PRACTICAL DENTAL METALLURGY. 

the base metal, it may be entirely removed. Mercury 
may be completely separated by roasting; it volatilizes at 
about 675° F. When endeavoring to expel it from old 
amalgam fillings, however, the plug should be heated to 
a bright red. 

ANNEALING AND TEMPERING.— Annealing is 
a process employed in the working of various metals and 
alloys to reduce the brittleness usually resulting from a 
rapid or important change of molecular structure, such 
as is produced by hammering, long continued vibration, 
rolling, and sudden cooling. Bell metal is brittle, and 
cracks under the hammer, cold as well as heated. If it 
be repeatedly brought to a dark-red heat and quickly 
cooled by immersion in water, its brittleness is so far 
decreased that it can be hammered and stamped. 

The dentist, in swaging a flat sheet of gold to conform 
to his dies, must stop at intervals and anneal the piece of 
metal to prevent its splitting under his blows and pressure. 

Wheels and axles of railway coaches, from the constant 
vibration to which they are subjected, become in course 
of time dangerously brittle; and they require to be re- 
worked and annealed anew to restore the required tough- 
ness to the material. 

It is said sudden changes of temperature have the 
effect, almost invariably, of rendering metals brittle. 
Gold, silver, platinum,, etc., should be heated for a re- 
arrangement of their molecular structure and allowed to 
slowly cool, rather than to be immediately plunged into 
a cold bath, if the best results are desired. Lead, tin, and 
zinc are annealed by immersion in water, which is made to 
boil and then cool slowly. Steel should not be annealed 
in an open fire, as the carbon which enters the iron as an 
element combines with the oxygen of the air to the detri- 
ment of the steel. 



ALLOYS. 91 

Annealing may be said to be the inverse process of — 

Tempering, which latter is the fixing of the molecular 
condition of steel by more or less sudden cooling from a 
particular temperature. 

Oxidation. — Alloys are usually more easily oxidized 
than their constituents. Mr. Makins says:* " The supe- 
rior oxidizability of one constituent of an alloy appears 
to be assisted by galvanic action set up. This is always 
the case where an electronegative, or acid-forming metal, 
is alloyed with an electropositive, or base-producing one. 
Chemical action is, therefore, generally more energetic 
on an alloy than upon a simple metal; and, indeed, metals 
which are untouched by an acid when alone will be acted 
upon by the same acid when alloyed with another which 
is soluble in the acid employed. Thus platinum is quite 
insoluble in nitric acid, but if it be alloyed with a large 
proportion of silver, it will be dissolved with the silver by 
the nitric acid, and that to the extent of a tenth of the 
weight of silver." 

Nearly all metals in a state of fusion have a tendency 
to dissolve a greater or less amount of their oxides; and 
this is particularly true of alloys, as then the metals are 
in a state of solution, a condition most favorable to chem- 
ical change. A striking illustration of this came under 
the author's notice in a dental-amalgam alloy prepared 
by Dr. S. E- Knowles, consisting of 2 parts tin and 1 
part each of silver and aluminum. There was no excep- 
tional difficulty in thoroughly blending the constitu- 
ents, and the alloy resembled the ordinary dental-amal- 
gam alloy when filed and ready for mercury, but upon 
the addition of mercury the oxidation of the whole was 
so rapid that a very considerable heat was evolved, and 
so complete that nothing remained but a black stain. 

* Makins' Metallurgy, p. G4. 



92 PRACTICAL DENTAL METALLURGY. 

"In some alloys, as those of copper and tin," Dr. 
Kirk says,* " as much as from 2 to 5 per cent, of the 
oxides formed will be dissolved, unless means are taken 
to prevent it." Such a solution of the oxides greatly 
diminishes the cohesive property of the alloy by prevent- 
ing perfect contact of the particles; hence, much of the 
strength and toughness of the mass are lost. 

The best preventative against this formation of oxides 
and their subsequent absorption is to protect the molten 
alloy by a layer of pulverized charcoal or some of the 
fluxes. A reduction- of much of the oxide formed may 
be effected by vigorous stirring with a stick of green 
wood. The careful addition of not more than % 000 to 
x /xooo parts of phosphorus has been found an excellent 
agent for the deoxidation of the oxides dissolved in 
bronze. 

The zinc and alloys used in the dental laboratory for 
making dies, after repeated melting and casting in con- 
tact with the air, often become thick and mushy from 
dissolved oxides; and their valuable working qualities 
are so seriously impaired that they fail to copy the fine 
lines of the mould and produce a perfect die. Their prop- 
erties may be restored to a great extent by melting under 
pulverized charcoal or tallow, and vigorously stirring with 
a stick of green wood. 

INFLUENCE OF CERTAIN METALS IN 
ALLOYS. — Certain metals when present in an alloy 
confer upon it definite properties which are in many in- 
stances characteristic; thus, in a general way, mercury, 
cadmium, and bismuth increase fusibility; tin, hardness 
and tenacity; antimony and arsenic, hardness and brit- 
tleness. 

* American System, of Dentistry, Vol. Ill, p. 801. 



ALLOYS. 93 

A SOLDER is an alloy or metal used for cementing or 
binding metallic surfaces or margins together, and the 
process is usually effected by heat. Ordinary solders are 
divided into hard and soft classes. 

The Hard Solders comprising those which require a 
red heat for their melting. 

The Soft Solders being those used by plumbers and 
tinsmiths, and consisting principally of lead and tin, with 
sometimes an addition of bismuth. 

Brazier s Solder, for uniting the surfaces of copper, 
brass, etc., is usually composed of copper and zinc, nearly 
equal parts, with a small addition of tin, and sometimes 
antimony. 

For fine jewelry, alloys of gold, silver, and copper are 
used; silver solder is employed for the inferior qualities, 
and even soft solder finds extensive use in jewelry estab- 
lishments. Silver is the proper solder for German silver 
articles, and gold for platinum. 

In Soldering, the surfaces or edges to be united must be 
kept free from oxidation and dirt. To keep them unoxi- 
dized during the operation several fluxes are used, such 
as dehydrated borax, or some of the reliable prepared 
compounds on the market, for gold, silver, brass, or 
copper soldering; rosin, or a solution of zinc chloride, for 
tin plate; zinc chloride for zinc, and rosin and tallow for 
lead and tin. 

Among the requirements of a good gold solder the 
most important are carat, color, strength, and fusing 
point. In fineness it should be equal, or nearly equal, to 
the plate, its color and strength as near as possible the 
same, while the fusing point should be a trifle lower — the 
nearer the melting point of the plate the better the results. 

To obtain these qualities, it is necessary to prepare a 
solder by the addition of some metal which will fuse at 



94 PRACTICAL DENTAL METALLURGY. 

a lower temperature than any of the constituents of the 
plate. Zinc is admirably suited for this purpose, and is 
generally used, since it permits of a solder as fine, or 
nearly as fine, as the plate. In addition to this it also 
possesses the advantage of yielding a less fluid solder 
than that of copper and silver, permitting it to bridge 
over slight spaces. This is very probably on account of 
the oxidatioa or volatilization which takes place, for it is 
observable that any subsequent fusing requires a greater 
heat. An advantage is also obtained here in this fact, 
since it enables more perfect second solderings with the 
same alloy. 

The process of soldering is a cementation by superficial 
alloying, and is admirably illustrated in the instance of 
soldering platinum bases for continuous-gum dentures. 
By means of the blow-pipe the pure gold is flowed over 
the surfaces of platinum, joining them, but if the joint is 
not well made, and the intervening space is filled with 
gold, it is not as strong as it might be. This, however, 
is all remedied during the process of baking the body and 
enamel, as the high heat required for this so diminishes 
the cohesive power of the platinum that it readily and 
completely alloys with the gold, producing a stronger 
joint of a platinum-gold alloy, which is observed to be 
the same color as the platinum. 

Autogenous Soldering is a process of soldering by 
direct fusion of the contiguous parts, without the inter- 
vention of a more fusible alloy. It is extensively used 
in large plumbing work. 

The sources of heat in soldering are the alcohol lamp 
or gas flame, intensified by the mouth or foot-bellows 
blow-pipe. In hard soldering the objects to be soldered 
and their investment are heated over a charcoal or gas 
furnace to equally heat all parts to a greater or less 



ALLOYS. 95 

extent preparatory to using the blow-pipe. When the 
furnace heating is carried to a high point the blow-pipe 
is needed but to slightly raise the temperature and direct 
the flow of the solder. Apparatus for heating and fusing 
metals and alloys have been studied under a special head, 
while the composition and management of various solders 
will be treated under appropriate heads, such as gold, 
silver, tin, etc. 

PREPARATION OF ALLOYS. —Casually this would 
seem but a simple task, but in order to produce an accu- 
rate result it is far from being as easy as it may seem. 

Most alloys are prepared by directly melting the metals 
together, but much skill, judgment, and experience are 
required to determine when it is best to add each constit- 
uent, and the amount of each to be used; to protect the 
molten mass, and to handle it generally. 

The metal having the highest fusing point is generally 
melted first, and the others are added in accordance with 
their points of fusibility. 

For making large quantities of an alloy the reverber- 
atory furnace is used, special precautions being taken to 
preserve a deoxidizing flame within the furnace. 

For preparing alloys in a small way a crucible is used, 
and the alloy is covered with a suitable flux to protect it 
from the action of atmospheric air. Four sources of loss 
must be guarded against: 1 — loss by oxidation; 2 — loss 
by volatilization; 3 — loss by chemical combination with 
the flux; 4 — loss by fracture or solution of the crucible. 

The first may be prevented by the use of one of the 
various fluxes,* or covering the surface with pulverized 
charcoal. The second loss usually occurs through an 
endeavor to alloy a metal of a high fusing point with one 
which fuses at a low temperature. Under such circum- 

*See chapter on Melting Metals. 



96 PRACTICAL DENTAL METALLURGY. 

stances the one requiring a high temperature should be 
fused first and well covered with flux melted to extreme 
fluidity ; the more fusible metal should then be added in 
as large a piece as convenient and quickly thrust beneath 
the molten surface. The third source of loss is prin- 
cipally caused by the use of borax as a flux for some base 
metals. It is well known that in much borax a portion 
of the boric acid is not perfectly saturated, and this is 
especially true of the prepared article; and if melted with 
some base metals the free acid is absorbed, which, with 
the sodium borate, forms double salts of a glassy nature. 
Hence, by fusing some metals and alloys under borax, a 
certain portion will be lost in chemical combination. The 
fouith cause is guarded against by careful selection of 
crucibles. If alloys of low fusing metals are to be made, 
the ordinary clay or Hessian crucible is all that is neces- 
sary, and, indeed, with proper care, noble metals may be 
alloyed in them without danger of loss; but they are 
subject to perforation by corrosive fluxes, allowing the 
molten alloy to escape. Therefore, for the preparation 
of expensive alloys from noble metals, the employment 
of tried graphite or graphite and clay crucibles often saves 
much trouble and expense. 

In some instances, especially when metals are known 
to form chemical combinations, it maybe best to melt the 
one of lowest fusing point first, and then dissolve the other 
components in it. Or, those of low fusing point may be 
melted in one crucible, while those more difficult of fusion 
are melted in another, then combined in the molten state. 

When two metals of varying specific gravity are alloyed 
the mass should not be allowed to become quiescent just 
before pouring. And if any incompatibility exists be- 
tween the metals, such as in the case of zinc and lead, 
accompanied by a great difference in specific gravity, an 



ALLOYS. 97 

intimate admixture should be effected by vigorously 
stirring the molten mass with sticks of soft, dry wood, 
which become more or less carbonized, according to the 
temperature of the mixture. In consequence of this dry dis- 
tillation of the wood there is evolved an abundance of 
gases, which, by ascending in the fused mass, contribute 
to its intimate mixture. The stirring should be con- 
tinued for some little time, and the alloy poured as 
quickly as possible. 

"Many alloys," says Mr. Brannt,* "possess the 
property of changing their nature by repeated remelting, 
several alloys being formed in this case, which show con- 
siderable differences, physically as well as chemically. 
The melting points of the new alloys are generally higher 
than those of the original alloy, and their hardness and 
ductility are also changed to a considerable extent. This 
phenomenon is frequently connected with many evils for 
the further application of the alloys, and in preparing 
alloys showing this property the fusion of the metals and 
subsequent cooling of the fused mass should be effected 
as rapidly as possible." 

Although most of the heavier metals are at present used 
in the preparation of alloys, copper, zinc, tin, lead, silver, 
and gold are more frequently employed than all others. 
Alloys containing nickel have become of great importance, 
as well as those in which aluminum forms a constituent. 

Mr. Brannt recommends for experimentation that 
metals be added to each other in certain quantities by 
weight, which are termed atomic weights, and claims that 
in this manner alloys of determined, characteristic prop- 
erties are, as a rule, produced; or, if such does not answer 
the demands of the alloy, the object maybe attained by 
taking two, three, or more equivalents of the metal, excep- 
tion being made in the cases of arsenic and such elements. 

* Metallic Alloys, p. 87. 



CHAPTER VI. 
LEAD. 

Plumbum. Symbol, Pb. 

Valence, II, IV. Specific gravity, 11.25 to 11.36. 

Atomic weight, 206.47. Malleability, 7th rank. 

Melting point, 325° (617° F.). Tenacity, lowest (8th) rank. 

Ductility, 8th rank. Chief ore, galenite. 

Conductivity (heat), 8.5. Conductivity (electricity), 8.32. 

(Silver being 100.) 

Specific heat, 0.0314. Crystals, octahedral. 
Color, bluish-white. 

OCCURRENCE.— This abundant and very useful 
metal is almost wholl}' obtained from its native sulphide, 
(1) Galenite (PbS) or galena, and is rarely, if ever, found 
free. Its other more widely distributed ores are (2) Ceru- 
site (PbC0 3 ), lead carbonate, sometimes called white-lead 
ore, and (3) Crocoisile (PbCr0 4 ), lead chromate. There 
is also a (4) Wulfenite (Mo0 4 Pb) and a (5) Sulphate 
(PbS0 4 ). Galenite often carries silver, as AgS, in suffi- 
cient quantities to be well worth extracting, the propor- 
tion of the noble metal varying from about 0.01 to 0.03 
per cent., and in rare cases amounting to 0.5 or 1 per 
cent. Such ore is called Argentiferous Galena. Lead 
ore frequently occurs accompanied by copper, iron pyrites, 
and zinc-blende. Galenite is found in the United States, 
Great Britain, Spain, and Saxony. 

REDUCTION OF GALENITE is effected in a rever- 
beratory furnace, into which the crushed lead ore is in- 
troduced and roasted for some time at a dull-red heat. 
In the roasting a portion of the lead sulphide is oxidized 
to the oxide and sulphate — 

PbS + 30=PbO+S0 2 and 
PbS+0 4 =PbS0 4 . 



LEAD. 99 

The contents of the furnace are then thoroughly mixed 
and the temperature raised, whereupon the sulphate and 
oxide react with the remaining sulphide, forming sul- 
phurous oxide and metallic lead — 

2PbO+PbS=SO,+ 3Pb and 
PbS0 4 + PbS=2S0 2 + 2Pb. 
Contaminating metals, which render the lead hard, are 
removed by melting and partially oxidizing in a rever- 
beratory furnace with a cast-iron bottom. 

EXPERIMENT No. 9.— (a)— Heat galenite with small pieces of iron 
or in an iron ladle. Result — metallic lead. 

PbS+Fe=Pb-fFeS. 

(b) Heat galenite on charcoal with sodium carbonate. Result— metallic 
lead. 

PROPERTIES.— Pure lead is a feebly lustrous, bluish- 
white metal, endowed with a high degree of softness and 
plasticity and almost entirely devoid of elasticity. A 
wire 1-10 of an inch in thickness is ruptured by a charge 
of about thirty pounds. It is said to be the least tena- 
cious of all metals in common use. Its specific gravity, 
as determined by Deville, is, for that "very slowly 
frozen," 11.254, and that " quickly frozen in cold water," 
11.363. It melts at 325°C* or 617° F. At a bright-red 
heat it vaporizes, and at a white heat boils. Its specific 
heat is .0314f , that of water at 0° C. being taken as 
unity. Lead exposed to ordinary air is rapidly tarnished, 
forming a suboxide, as is thought; but this thin film 
once formed is very slow in increasing. The same sup- 
posed suboxide is formed upon lead kept in a state of 
fusion in the presence of air, when at the same time the 
metal rapidly absorbs oxygen; then the monoxide (PbO) 
is formed, the rate of oxidation increasing with the tem- 
perature. By slowly cooling, lead may be obtained in 

* Rudberg. 
+ Regnault. 



100 PRACTICAL DKNTAL METALLURGY. 

octahedral crystals. Dilute acids, with the exception of 
nitric, act but slowly on lead. 

DENTAL APPLICATIONS.— Its chief dental use 
is in the laboratory as a counter-die. It may be rolled 
into a thin foil, and at one time was used for filling 
carious teeth, and in conical points is now used in filling 
the apices of pulp-canals. It is an important component 
of soft solders and various alloys.* 

COMPOUNDS WITH OXYGEN.— There are four 
compounds of lead and oxygen: 

The Diplumbic Oxide, or Lead Suboxide, Pb 2 0, a gray 
pulverulent substance, is formed when the monoxide is 
heated to dull redness in a retort, and is supposed to cor- 
respond with the dull coating formed on bright, freshly 
cut surfaces of lead when left exposed to the air. 

EXPERIMENT No. 10.— Melt old, partially oxidized lead in a ladle 
under powdered charcoal — metallic lead. 

The Monoxide, Litharge or Massicot, PbO, is very 
heavy, and of a delicate straw-yellow color, slightly 
soluble in water, melting at a red heat, with a tendency 
to crystallize on cooling, and is easily reduced when 
heated with organic substances of any kind containing 
carbon or hydrogen. It is the product of the direct oxi- 
dation of the metal, but is more conveniently prepared 
by heating the carbonate to dull redness. 
PbCO s ( + heat) — Pb0 + C0 2 . 

EXPERIMENT No. 1 1.— Heat the monoxide in reducing flame on char- 
coal — metallic lead. v 

The Dioxide, Puce or Brown Lead Oxide, Pb0 2 , is a 
heavy brown powder, insoluble in water, having an acid 
reaction, and may be regarded as the anhydride of plum- 
bic acid, H 4 Pb0 4 . It is easily obtained by digesting the 
red oxide in nitric acid. 

* See Literature — Lead. 



LEAD. 101 

Red Oxide, or Red Lead ', is a compound of the mon- 
and dioxides, not very constant in its composition, but is 
generally regarded as having the formula 2PbO,Pb0 2 
(Pb 3 4 ). It is a heavy, bright-red powder, and may be 
regarded as lead plumbate, Pb 2 Pb0 4 . It is used as a 
cheap substitute for vermilion. When treated with 
dilute nitric acid the monoxide dissolves, forming soluble 
lead nitrate, leaving the puce-colored oxide behind. It 
is prepared by exposing the monoxide, which has not 
been fused, for a long time to the air at a very faint red 
heat. 

EXPERIMENT No. 12.— To a small amount of red lead placed in a test- 
tube add a small quantity of dilute HNO... The 2PbO is dissolved and the 
PbO, is left. 

EXPERIMENT No. 13.— Heat litharge to red heat in the presence of air 
— red lead. (Note. — The product soon loses its additional oxygen when heated 
but for a short time, returning to the yellow oxide.) 

ACTION OF ACIDS ON LEAD.— The presence of 
carbonic acid in a water does not affect its action on lead. 
Aqueous non-oxidizing acids generally have little or no 
action on lead in the absence of air. 

Sulphuric Acid, when dilute (20 per cent, solution or 
less), has no action on lead, even when air is present, nor 
on boiling. Stronger acid doss act, slowly in general, 
but appreciably, the more so the greater its concentra- 
tion and the higher its temperature. Pure lead is more 
readily acted upon than that contaminated with antimony 
or copper. Boiling concentrated sulphuric acid converts 
lead into the sulphate, with evolution of sulphurous 
oxide. 

EXPERIMENT No. \4.— To small pieces of lead foil in a test-tube add 
concentrated sulphuric acid and boil. 

Pb-f2H.,SO +PbSO + + SO.,-(-2H,0. 

Nitric Acid. — The metal is readily dissolved in dilute 
nitric acid, nitrogen dioxide being evolved and plumbic 
nitrate formed. 



102 PRACTICAL DENTAL METALLURGY. 



EXPERIMENT No. 15.— To several pieces of lead foil in a test-tube add 
dilute nitric acid and warm to hasten action. 

3Pb-f8HNO. s +3Pb (N0. J )., + 2N0-f4H,0. 
(Preserve) 

Hydrochloric Acid. — Strong and hot hydrochloric 
acts but slowly upon lead, forming the dichloride and 
liberating hydrogen. 

EXPERIMENT No. 16.— To small pieces of lead foil in a test-tube add 

strong HC1 and boil. 

Pb+2HCl + PbCL+2H. 

ACTION OF AQUEOUS REAGENTS ON LEAD. 

— Water, when pure, has no action on lead per se. In 
the presence of free oxygen (air), however, the lead is 
quickly attacked, forming a hydrated oxide, Pb2HO= 
PbOH 2 0, which is appreciably soluble in water, render- 
ing the liquid alkaline. When carbonic acid is present 
the dissolved oxide is soon precipitated as basic carbon- 
ate — PbC0 3 (which is slightly soluble in water containing 
carbon dioxide) — so there is room made, so to say, for 
fresh hydrated oxide, and the corrosion of lead pro- 
gresses. Now, all soluble lead compounds are strongly 
cumulative poisons; hence the danger involved in using 
lead pipes or cisterns in the distribution of PURE waters. 
We emphasize the word " pure," because experience 
shows that the presence in water of even small propor- 
tions of bicarbonate or sulphate of lime prevents its action 
on lead. This little sulphate, almost invariably present, 
causing the deposition of a very thin but closely adherent 
film of lead sulphate upon the surface of the metal, 
which protects it from further action. 

ALLOYS. — Pure lead unites with almost all metals. 

Mercury readily amalgamates with it, and, in proper 
proportions, crystallizes, forming a very white but brittle 
alloy. This union is said to be of a definite chemical 
proportion, and is expressed as Pb 2 Hg. Very small 



LEAD. 103 

quantities of lead admixed with the noble metals destroy 
completely their malleability, and hence renders them 
unworkable. It is said that l-1920th part of lead in 
gold will greatly impair its coining property, and that 
gold containing l-500th part of lead is "rendered unfit 
for coinage. " The gold drawer in the dental laboratory 
is often so situated that it is almost impossible to pre- 
vent particles of lead from accumulating with the gold 
scraps and filings. These, however, may be easily re- 
moved by roasting with potassium nitrate and sulphur. * 

Silver in certain proportions with lead forms an alloy 
which has a lower fusing point than that of lead. Pat- 
tinson, taking advantage of this fact, invented his proc- 
ess for recovering the silver from argentiferous galena. A 
quantity of the silver-lead ore is melted in one of a series 
of iron pots. After complete fusion it is allowed to 
slowly cool, when the poorer lead crystallizes and is 
ladled off to another pot, leaving the rich silver-bearing 
lead behind. This is carried on through the whole series 
of some twelve pots, until the lead-silver alloy has been 
reduced to proportions by which the noble metal may be 
recovered by the process of cupellation.f 

Platinum with equal weight of lead gives a purplish- 
white, brittle, and granular alloy. So great is the 
affinity these metals have for each other that lead oxide 
heated in a platinum crucible with reducing flux is 
broken up and the lead combines with the platinum 
vessel. I^ead can only be separated from platinum by 
the humid process of refining platinum. 

Palladium and lead form a green alloy which is very 
hard and brittle. 

The more common alloys of lead are those with tin, 
antimony, etc. 

* See chapter on Gold, 
t See chapter on Silver. 



104 PRACTICAL DENTAL METALLURGY. 



Tin unites with lead in almost any proportion with 
slight expansion.* 

The following table gives an idea of the melting points 
of alloys of lead and tin : 

An Alloy of— Fuses at— 
Lead 1, Tin 2 340° F. 

" 1, " (i 382° F. 

" 2, " 1 442° F. 

" 4, " 1 498° F. 

" 17, " 1 557° F. 

With tin 1 part and lead 5 partsf Dr. Haskell makes 
counter-dies to be used with his Babbitt-metal dies. 
It fuses at a lower temperature than the die alloy, and 
also has the advantage of being harder than lead, which 
he claims is too soft for counter-dies. Tin-lead alloys 
are used largely in soldering. 

The following are compositions and melting points of 
frequently used compounds^: 

Grade. Tin. I^ead. Melts at — 

Fine Solder... 2 1 340° F. 

Common " .... 1 1 370° F. 

. Coarse " . . . . 1 2 442° F. 

Pewter may be said to be substantially an alloy of the 
same two metals; but small, quantities of copper, anti- 
mony, and zinc are frequently added. Common pewter 
contains about 5 parts of tin for 1 of lead. In France 
a tin-lead alloy, containing not over 18 per cent, of 
lead, is recognized by law as being fit for measures for 
wine or vinegar. " Best pewter" is simply tin alloyed 
with a mere trifle (}4 per cent, or less) of copper. 

Antimony. — L,ead contaminatedwith small proportions 
of antimony is more highly proof against vitriol than the 

* Kuppfer. 

| The author has found the fusing point of this alloy to be S7b r F. 

X Tomlinson. 



LEAD. 105 

pure metal. An alloy of 83 parts of lead and 17 parts of 
antimony is used as type metal; other proportions are 
used, however, and other metals added besides antimony 
(e. g., tin, bismuth) to give the alloy certain properties. 

Arsenic renders lead harder. An alloy made by the 
addition of about } y 56 of arsenic is used for making shot. 

Lead forms a very important part in " fusible alloys."* 

TESTS FOR LEAD IN SOLUTION.— In testing 
various solutions, first pour some of that which you have 
reason to suspect in a test-tube, to the height of an inch 
or so, and add a few drops of the selected reagent. 
Sometimes the precipitate is soluble in an excess of this 
reagent, and sometimes in excess of either solution or 
reagent. If there be reason to suspect either, proceed 
cautiously, adding but a drop at a time, until a sufficient 
precipitate has been thrown down. If the first few drops 
of the reagent added cause a precipitate which is imme- 
diately redissolved, it shows that it is soluble in an 
excess of the solution, and if it be also soluble in an 
excess of the reagent, an equilibrium must be attained. 
After the precipitate has thoroughly settled note its color 
and general appearance; then decant the supernatant 
liquid as thoroughly and carefully as possible, and divide 
the precipitate in as many other test-tubes as may be 
desired for testing its solubility in the various reagents. 

Sulphuretted hydrogen is one of the most important 
reagents used in tests for salts of metals in solution. To 
the suspected solution add, drop by drop, the saturated 
solution of sulphuretted hydrogen (U 2 S); a black pre- 
cipitate is quickly formed, which is insoluble in an excess 
of the reagent. To the suspected solution add a few drops 
of ammonium hydrosulphide, (H 4 N)HS; a black precipi- 
tate, insoluble in an excess of the reagent, is formed. 

* See chapter on Bismuth. 



106 PRACTICAL DENTAL METALLURGY. 



Potassium hydrate or ammonia throws down a white 
precipitate — hydrated oxide. This is soluble in an ex- 
cess of the potassa, but not of the ammonia. 

Alkaline carbonates precipitate the white plumbic 
carbonate, which is quickly blackened by sulphuretted 
hydrogen. 

Sulphuric acid is a characteristic test, precipitating a 
white sulphate. 

Hydrochloric acid or a chloride gives a white pre- 
cipitate soluble in an excess of potassa. 

EXPERIMENT No. 1 7.— Test a lead-salt solution as above. 

BLOW-PIPE ANALYSIS.— A lead-salt is easily re- 
duced on a piece of charcoal before the blow-pipe, a bead 
of lead ultimately resulting in the center of the point of 
fusion, around which the charcoal will be seen to have 
absorbed a portion of the yellow monoxide of lead. The 
bead may be readily recognized as metallic lead, which 
is soft and may be readily flattened or cut with a knife. 
"If the lead contains silver, the latter is easily detected 
by the use of bone-ash. Fill a bowl-shaped cavity in 
the charcoal with finely powdered bone-ash, pressed 
down well, so as to fill the cavity with a compact mass, 
smooth, and slightly hollowed on the surface. In this, 
place a small quantity of the lead, hold the charcoal 
horizontally, and direct the extreme point of the outer 
(oxidizing) flame upon the metal. The bone-ash will 
absorb the lead oxide formed, leaving a metallic globule 
of silver. The latter may be covered with a thin film of 
oxide, showing rainbow tints. When the color ceases, 
and the globule no longer diminishes in size, it is pure 
silver. The process is hindered by the presence of tin."* 

On charcoal in either flame lead is reduced to a malle- 
able metal, and yields near the assay a dark lernon- 

*Dr. Clifford Mitchell. 



LEAD. 107 

yellow coat, sulphur-yellow when cold, and bluish-white 
at border. 

With bismuth flux: On plaster, a chrome-yellow coat, 
blackened by ammonium sulphate. 

Interfering Elements. — Antimony. — Treat on coal 
with boracic acid, and treat the resulting slag on plaster 
with borax flux. 

Arsenic Sulphide. — Remove by gentle O. F. 

Cadmium. — Remove by R. F. 

Bismuth. — Usually the bismuth flux test on plaster 
is sufficient. In addition the lead coat should color the 
R. F. blue. 

ELECTRO-DEPOSITION OF LEAD.— In a solu- 
tion of hyponitrite, nitrate or acetate of lead, zinc re- 
ceives a coating, or its place may be taken entirely by 
the lead. 

EXPERIMENT No. 18.— Dissolve one dram of the nitrate or acetate 
of lead in about two pints of distilled water and put the solution in a bottle. 
Suspend a piece of granulated zinc or a spiral of zinc wire in the center of the 
solution and let it stand. The lead will be deposited slowly in a crystalline 
form, known as arbor phimbi. At the same time the zinc will pass into solu- 
tion, the lead simply replacing the zinc. After the tree has been formed 
filter off some of the solution and see whether or not zinc is contained in it. 
There will probably be some lead left. In order to detect the zinc the lead 
w T ill have to be removed. This may be done by adding sulphuric acid (form- 
ing the sulphate) and alcohol (to prevent its being redissolved). Filter off the 
lead sulphate, and to the filtrate add just enough ammonia to neutralize the 
sulphuric acid, and then test with ammonium hydrosulphide; white zinc sulphide 
is precipitated. 



CHAPTER VII. 

ANTIMONY. 

Stibium. Symbol, Sb. 

Valence, III, V. Specific gravity, 6.715. 

Atomic weight, 119.95 Malleability, brittle. 
Melting point, 425° (797°F.). Tenacity, brittle. 

Ductility, brittle. Chief ore, stibnite. 

Specific heat, 0.050S. Crystal, rhombohedral. 
Color, bluish-white. 

OCCURRENCE —Antimony is found in the metallic 
state to a small extent in many of the localities from which 
its ores are derived. It occurs alloyed with other metals, 
such as silver, nickel, copper, and iron, and usually 
contaminated with arsenic. Commercial antimony is 
obtained almost entirely from its chief ore stibnite, the 
sulphide, Sb 2 S 3 , which is found in great abundance in 
Borneo, New Brunswick, and Nevada. This ore usually 
occurs in veins, and has a leaden-gray color, with a 
metallic, sometimes iridescent, luster. 

REDUCTION.— The metal is easily reduced by heat- 
ing the ore in a furnace with about half its weight in 
scraps of metallic iron, whereupon it gives up its sulphur, 
which unites with the iron, forming ferrous sulphide, and 
liberates antimony. 

Sb 2 S 3 + 3Fe=Sb 2 + 3FeS. 

The metal is so frequently contaminated with arsenic 
that it cannot be safely used for dental purposes until it 
has gone through a refining process. 

Chemically pure antimony may be best obtained as 
follows : — Four parts of metallic antimony are powdered 
with two parts of sodium carbonate and five parts sodium 
nitrate; the whole is then heated. The arsenic, if any 



ANTIMONY. 109 



be present, and antimony are converted to the oxides at 
the expense of the oxygen of the nitrate, and then 
sodium arsenate and antimonate are formed with the 
sodium of the carbonate. Upon cooling, these com- 
pounds are powdered and thrown into boiling water; the 
soluble arsenate is dissolved, while the insoluble anti- 
monate remains. The latter after having been thoroughly 
washed with hot water is dried and heated with half its 
weight of potassium bitartrate. The product of this 
fusion is then broken up and cast into water, when the 
potassium of the tartar oxidizes, liberating hydrogen 
and leaving the antimony as a powder contaminated with 
any iron or lead that may have been contained in the 
original metal. These latter are gotten rid of by heating 
about one-third of the powder with nitric acid, oxidizing 
it; this portion is then dried, mixed with the remainder 
and fused in a covered crucible; pure antimony separates 
and subsides under a slag composed of these foreign 
oxides. 

PROPERTIES.— Pure antimony is a brilliant, some- 
what iridescent, bluish-white metal, readily crystallizing 
in rhombohedrons, which form large stellate figures on the 
fused surface when cooled. It fuses at 425° C. (797°F.)» 
and may be distilled at a white heat in an atmosphere of 
hydrogen. When heated to redness it takes fire, burning 
with a brilliant white flame. It undergoes no change in 
air at ordinary temperatures, but is easily oxidized when 
heated to fusion. It is an important metal in the manu- 
facture of alloys, increasing their hardness even when 
mixed in very small quantities. The finely powdered 
metal takes fire spontaneously when thrown into chlorine 
gas, forming chlorides. 

COMPOUNDS WITH OXYGEN.— Antimony forms 
two distinct oxides : 



110 PRACTICAL DENTAL METALLURGY. 

The Trioxide, or Antimonous Oxide ', Sb 2 3 , occurs 
native, though rarely. It may be prepared by burning 
metallic antimony at the bottom of a large red-hot cruci- 
ble. It is a pale buff-colored powder, fusible, volatile, 
of basic reaction, and absorbing oxygen at a high heat is 
changed into the tetroxide, or Sb 2 3 ,Sb 2 O s . When 
boiled with potassium bitartrate it is dissolved, and the 
solution yields on evaporation crystals of tartar emetic^ 
KSbOC 4 H 4 6 . 

The Pentoxide, or Antimonic Oxide, Sb 2 5 , is obtained 
by the action of strong nitric acid on antimony. It is a 
pale straw-colored powder, of acid reaction, insoluble in 
water or acids, decomposes on being heated, passing to 
the intermediate oxide, Sb 2 3 ,Sb 2 O s . 

The Intermediate Oxide, or Tetroxide, Sb 2 4 , as it is 
sometimes called, Sb 2 3 , Sb 2 O s , is obtained by heating the 
pentoxide in the air, and is recognized as an infusible, 
non-volatile and insoluble, grayish-white powder. 

ACTION OF ACIDS ON ANTIMONY.— Hydro- 
chloric acid, boiling and concentrated, slowly dissolves 
powdered antimony, forming antimonous chloride and 
liberating hydrogen- — 

Sb+3HCl=SbCl 3 + 3H, 
but when the metal is in the compact state it resists 
this acid. 

Sulphuric acid, boiling and concentrated, slowly con- 
verts it into antimonous sulphate with an evolution of 
sulphur dioxide — 

2Sb+ 6H 2 S0 4 =Sb 2 3S0 4 + 6H a O + 3S0 2 , 

Nitric acid rapidly oxidizes the metal, the dilute acid 
forming chiefly antimonous oxide — 

2Sb+ 2HN0 3 =Sb 2 3 -f H 2 + 2NO, 

while the concentrated form yields some antimonic oxide — 

6Sb+ 10HNO 3 =3Sb 2 O 5 + 5H 2 0+ 10NO. 



ANTIMONY. Ill 



For the most part the intermediate is the result of this 
action — 

6Sb+8HN0 3 =3Sb 2 4 + 4H 2 + 8NO. 

Nitro-hydrochloric acid converts it into soluble 
antimonous chloride and insoluble oxides. 

Tartaric acid in a boiling solution slowly dissolves 
precipitated antimony— 

2Sb+H 2 (C 4 H 4 6 ) + 2H 2 0=(SbO) 2 C 4 H 4 6 +6H. 

Alkalis do not dissolve it. 

ALLOYS. — The metal is chiefly valuable for the alloys 
it yields with other metals, and, as has been said, pos- 
sesses the quality of increasing the hardness of those 
alloys. Antimony also causes expansion in most alloys, 
thereby copying fine lines and sharp casts; hence, its 
great value in the manufacture of type. In many cases 
it renders the alloy very brittle, and is especially injuri- 
ous to the noble metals or copper, destroying their mal- 
leability, ductility, etc. 

Mercury. — The amalgam of antimony is soft and 
easily decomposed. Experiments have been made, with 
a view to using this element in dental-amalgam alloys, 
but to no profit. 

Gold. — One grain of antimony to 2000 will greatly 
injure the malleability of gold. 

Copper containing l-1000th of this metal can no longer 
be worked for sheet-brass. 

Tin. — Antimony is added to tin alloys to give hard- 
ness and expansion, but renders most of them very 
brittle. 

Bismuth forms with antimony a grayish, brittle, and 
lamellar alloy. In order to remove the brittleness vary- 
ing quantities of tin are added, as is also lead, and both. 
The fusibility then rather increases, instead of decreasing. 



112 



PRACTICAL DKNTAL METALLURGY. 



Some alloys containing antimony: 

Cliche metal, tin 48, lead 32.5, bismuth 9, and 
antimony 10.5. 

Babbitt metal, copper 4, tin 12, and antimony 8, 
melted separately. The antimony is added to the tin, 
then the copper, and 12 parts more tin after fusion. 

TVPE METAL— TABLE OF COMPOSITION.* 



Metal 






Parts. 








i. 


ii. 


III. 


IV. 


v. 


Antimony 


3 
1 


10 
2 


70 
18 

2 


6 
4 


100 
30 

8 






1 


2 


Zinc 






90 




Tin 






10 


20 








8 















Britannia Metal (Wagner's). — Tin 85.64, antimony 
9.66, copper 0.81, zinc 3.06, and bismuth 0.83. 

Queen's Metal. — Tin 88.5, antimony 7.1, copper 3.5, 
and zinc 0.9. 

TESTS FOR ANTIMONY IN SOLUTION.— 
Sulphuretted Hydrogen added to an acidulated solu- 
tion of antimony occasions an immediate precipitate of 
very characteristic orange-red color. 

Potassa, or ammonia, or their carbonates, throw down 
a bulky white hydrate, of which that formed by potassa 
is soluble in excess of alkali, but the hydrate formed by 
the ammonia or alkaline carbonates is nearly insoluble. 

If a hydrochloric acid solution be treated with a quantity 
of water, an immediate precipitate of oxychloride falls, 
soluble in tartaric acid distinguishing it from bismuth. 
3SbCl 3 + 4H 2 0=Sb 3 4 Cl+ 8HC1. 

* Table from Brannt. - 



ANTIMONY. 113 



ELECTRO-DEPOSITION OF ANTIMONY.— 

Antimony may be electro-deposited by simple immer- 
sion by placing a piece of zinc in contact with a piece of 
antimony in a solution of the chloride of antimony, or a 
piece of platinum may receive a coating of antimony on 
being immersed in a solution of the chloride in contact 
with a piece of tin. 

It may also be deposited from an acid solution of the 
chloride by the separate current process, producing ex- 
plosive antimony. 



CHAPTER VIII. 
TIN. 

Stannum. Symbol, Sn. 

Valence II, IV. Specific gravity, 7.29. 

Atomic weight, 117.69. Malleability, 4th rank. 

Melting point, 228° (442° F.). Tenacity, 7th rank. 

Ductility, 7th rank. Chief ore, tinstone. 

Conductivity (heat) 14.5. Conductivity (electricity), 12.36. 

(Silver being 100.) 

Specific heat, 0.0562. Crystals, isometric and quadratic. 
Color, brilliant white. 

OCCURRENCE. — Tin occurs chiefly as ti?istone, cassit- 
erite, or native oxide, Sn0 2 , which forms in very hard 
quadratic crystals, usually discolored by the presence of 
ferric or manganic oxide. The pure ore is colorless and 
very scarce. Another native form known as " wood tin " 
occurs in roundish masses, with a fibrous, radiating 
fracture. The metal is rarely, if ever, found free. The 
ore is mined from veins or layers within the older crys- 
talline rocks and slates, associated with copper ore, iron 
arsenide and other minerals, and as alluvial deposits, 
mixed with rounded pebbles, in the beds of streams. 
The former is called mine-tin, and the latter stream-tin. 

REDUCTION.— The ore is first washed to separate it 
from earthy impurities, and then stamped, and again 
washed to separate the lighter gangue. It is then roasted 
at a low heat to volatilize the arsenic and sulphur, with- 
out at the same time fusing the ore. The copper ore, 
copper pyrites, is, during this time, joined with subse- 
quent exposure to air and moisture, changed to copper 
sulphate, and is then dissolved out by water, the copper 
afterwards being reduced by iron and thereby saved. 
The ore is finally washed to separate all lighter oxides, 



TIN. 115 

and is then ready for smelting. The purified ore, known 
as "black tin," is mixed with about 15 to 20 per cent, 
of anthracite "smalls," the mixture moistened to pre- 
vent its being blown off by the draft, then fused in a 
reverberatory furnace for five or six hours, and, after 
thorough stirring, the metal is run off — 
Sn0 2 + 2C=Sn+2CO. 

The tin obtained from Malacca is almost chemically 
pure, while that from England almost invariably contains 
traces of arsenic and copper. Most of the tin consumed 
in this country is shipped from Singapore, having been 
mined from the Malacca regions. Two varieties of the 
commercial metal are known, called grain and bar-tin- 
The first is the better; it is prepared from the stream ore. 

EXPERIMENT No. 19. — Roast tin oxide in crucible with charcoal or 
heat on charcoal block with sodium carbonate in reducing flame— globule 
of tin. 

Pure Tin. — Tin used in dental operations should be 
chemically pure. Much of that which we have just de- 
scribed is still greatly contaminated with arsenic, copper, 
iron, etc., and to obtain it pure a further refining process 
must be gone through with. For this purpose good 
commercial tin may be dissolved in hydrochloric acid. 
Hydrogen is evolved, and the metals are all converted 
into chlorides, with the exception of antimony and 
arsenic. If either of these be present it will combine 
with hydrogen, forming a gas and be evolved. The 
liquid is now evaporated to a small bulk, and to it is 
added nitric acid, which will convert the tin into the 
insoluble, white, crystalline, metastannic acid, H IO Sn 5 O l5 . 
The whole is now evaporated to dryness, washed with 
water acidulated with hydrochloric acid, filtered, re- 
washed, dried, and melted in a crucible with charcoal, 
when a button of pure tin will result. 



116 PRACTICAL DENTAL METALLURGY. 

EXPERIMENT No. 20.— Dissolve commercial tin in hydrochloric acid , 
evaporate and add nitric acid. Kvaporate to dryness and add water acid- 
ulated with hydrochloric acid, wash, place on filter and rewash, melt in 
crucible with charcoal, and obtain pure tin button. 

PROPERTIES.— Pure tin is white (except for a slight 
tinge of blue); it exhibits considerable luster, and is not 
subject to tarnishing on exposure to normal air. It is 
soft and exceedingly malleable; indeed, it is said it may 
be beaten into foil 1-40 of a mm. in thickness; at 100° C. 
it may be drawn into wire, but is almost devoid of 
tenacity. That it is elastic, within narrow limits, is proven 
by its clear ring when struck with a hard body under 
circumstances permitting free vibration. Though it is 
seemingly amorphous, it has a crystalline structure con- 
sisting of an aggregate of quadratic octahedra, hence the 
crackling noise known as the "tin cry" which a bar of 
tin emits on being bent. This structure can be rendered 
visible by superficial etching with dilute acids. The 
crystalline structure must also account for the strange 
fact that an ingot, when exposed to the temperature of 
— 39° C for a sufficient length of time, becomes so brittle 
that it falls into powder under pestle or hammer, and, 
indeed, sometimes crumbles into powder spontaneously. 
At some temperature near its fusing point it again 
becomes brittle. Tin fuses at 228° (442.4° F.).* At a 
red heat it begins to volatilize slowly; at 1600° to 1808° 
C. it boilsf and may be distilled. The hot vapor produced 
combines with the oxygen of the air, forming the white 
oxide, Sn0 2 . The specific gravity of the cast metal is 
7.29 to 7.299; of that which has been crystallized by the 
galvanic current from solutions 7. 178. J Its specific heat 
is 0.0562. 

*Rudberg. 
f Williams. 

JW.H. Miller. 



TIN. 



117 



DENTAL APPLICATIONS.— Tin-foil is very highly 
recommended as a filling-material for carious teeth, on 
account of the ease with which it may be inserted; its sup- 
posed therapeutic effect (which is doubtful), and because 
of its comparatively low conducting power of heat, tin, 
as compared to silver, which is taken as the unit, being 
14.5, while gold rises to 53.2, and, absolutely pure gold 
much higher. In the conduction of electricity the com- 
parison is still greater: tin 12.36 and gold 77.96.* The 
combination of tin and gold foil is said to have a very 
low conducting power of heat. It is claimed that dis- 
integration of the tooth structure by galvanic action at 
the margins of the cavity so filled is rendered impossible, 
from the fact that any such action is confined to the 
metals which form a closed circuit, tin-foil being more 
electropositive to gold than tooth structure. It is also 
claimed that consolidation of the two metals occurs sub- 
sequent to their insertion as a filling. Of this Dr. W. D. 
Miller, Berlin, says: "Without entering into a pro- 
longed discussion of the causes of this consolidation, I 
will say that it is owing to electro-chemical process, 
through which the tin is dissolved and redeposited upon 
the surface of the gold. By this means the material 
becomes rigid and all parts of the filling thoroughly 
bound together. * * * It has neither therapeutic 
nor antiseptic action. "f (See Addendum.) 

Models of tin are used to vulcanize upon, and plaster 
models are often covered with tin-foil to give a clear and 
finished appearance to the denture after the process of 
vulcanization. 

COMPOUNDS WITH OXYGEN.— There are two 

oxides of tin : 

* Figures from Matthiessen. 
f Cosmos, Vol. XXXII, p. 714. 



118 PRACTICAL DENTAL METALLURGY. 

Tin Monoxide, or Stamious Oxide, SnO, is a black- 
ish-brown powder of feeble basic reaction prepared by- 
heating stannous hydrate, Sn2HO, in an atmosphere of 
carbon dioxide. It is unstable, and burns when heated 
in the air, becoming stannic oxide. 

Tin Dioxide, or Stannic Oxide, Sn0 2 , occurs native 
as tinstone, or cassiterite, the common ore of tin, and is 
easily formed by heating tin, stannous oxide, or stannous 
hydrate, in contact with air. According to the manner 
in which it may be prepared, it is either a white or yel- 
lowish-white amorphous powder, or it may be obtained 
crystalline. It is infusible and insoluble in the acids or 
alkalis, and is known as " polishing putty," being used 
for polishing glass, hard metals, granite, and similar 
substances. It forms two isomeric hydroxides (stannic 
and metastannic), which differ somewhat in their prop- 
erties; both, however, are acids, and capable of ex- 
changing their hydrogen for metal, thereby forming salts: 

Stannic Acid, H 2 Sn0 3 , is precipitated by an alkali 
from stannic chloride as a white powder, soluble in the 
stronger acids and alkalis, and is capable of exchanging 
the whole of its hydrogen for metal-forming stannates, 
as: Na 2 Sn0 3 . These salts are quite stable. 

Metastannic Acid, H IO Sn 5 O l5 , may be written 
H 2 Sn0 3 , is prepared as a white crystalline powder by the 
action of dilute nitric acid upon tin. It is insoluble in 
water and the acids, but dissolves slowly in the stronger 
alkalis, and has the property of exchanging only one-fifth 
of its hydrogen for metal-forming metastannates, very- 
unstable, as K 2 H 8 Sn 5 O l5 . 

ACTION OF ACIDS ON TIN.— The three mineral 
acids act upon tin. 

Sulphuric acid, concentrated, acts rather energetic- 
ally at first, but, owing to the stannic sulphate coating 



TIN. 119 

which is soon formed, its action is greatly hindered. 
The dilute form acts slowly, but converts the whole of 
the tin into stannic sulphate with a liberation of hy- 
drogen. 

Sn + H 2 S0 4 =SnS0 4 -f-2H. 

EXPERIMENT No. 21.— Place small pieces of tin-foil in test-tube, and 
add dilute sulphuric acid— stannic sulphate. 

Nitric Acid. — In its concentrated form this acid acts 
but feebly upon tin, and, if heated, produces the nitrate; 
but the dilute is energetic, and, instead of dissolving, 
oxidizes it into the crystalline powder, hydroxide, known 
as metastannic acid — H IO Sn 5 O l5 . 

3Sn + 4HN0 3 =3Sn0 2 + 2H 2 + 4NO, and then 

5Sn0 2 + 5H 2 0=H IO Sn 5 O l5 . 

EXPERIMENT No. 22.— To small pieces of tin in test-tube add dilute 
nitric acid — metastannic acid. 

Hydrochloric Acid. — Strong, warm hydrochloric acid 
acts energetically upon tin, the cold and dilute forms 
acting more slowly, but converting it into stannous 
chloride and liberating hydrogen. 

Sn + 2HCl=SnCl 2 + 2H. 

EXPERIMENT No. 23.— Dissolve tin in hot, strong, hydrochloric acid 
adding more tin than will be dissolved. Filter and preserve. 

Nitro-hydrochloric acid dissolves tin very energetic- 
ally, producing stannic chloride, SnCl 4 . 

Sn+4C1 (nascent chlorine)=SnCl 4 . 

EXPERIMENT No. 24.— To small pieces of tin-foil in a test-tube add a 
small amount of nitro-hydrochloric acid — stannic chloride is formed. Filter 
and preserve. 

Caustic Alkalis. — Boiling solutions of caustic soda or 
potassa act upon tin, producing stannates with an evo- 
lution of hydrogen. 

Sn+2KHO + H 2 0=K 2 Sn0 3 + 2H 2 . 



120 PRACTICAL DKNTAL METALLURGY. 

ALLOYS. — Mercury and tin readily unite as an amal- 
gam, under ordinary circumstances, and, it is said, form a 
definite chemical compound having the formula, Sn 2 Hg. 

Tin is a very important component of dental-amalgam 
alloys.* Of it Dr. J. Foster Flagg says, in his work on 
Plastics and Plastic Filling : "All such alloys as I should 
favorably regard, have from 35 to 48 per cent, of tin; it 
is found that by the addition of copper and gold, both 
antagonists of "shrinkage," the most deleterious of the 
effects of tin can be counterbalanced; that under this 
control sufficient silver can be used to obviate a detri- 
mental loss of edge-strength; that the retardation of 
11 setting" is prevented, and that the tin not only loses 
its power for harm, but becomes an ingredient of mani- 
fold utility; it greatly augments the facility of amal- 
gamation; it aids in producing a good color and in 
preventing discoloration; and it diminishes conduc- 
tivity." 

The amalgam of tin is also largely used in the manu- 
facture of mirrors. 

Gold and tin form a malleable alloy, provided the tin 
be pure and does not exceed in quantity 10 per cent. 

Platinum and tin in equal proportions form a hard, 
but brittle, alloy, fusing at a comparatively low tempera- 
ture. 

Palladium, says Mr. Makins, forms a very brittle 
alloy with tin. 

In view of the fact that gold, platinum, and palladium 
so readily unite with tin to form alloys whose 
fusing points are so comparatively low, and in 
view of the behavior of tin with other metals, 
and of metals in general toward each other, there 
is little reason to doubt a chemical affinity of tin 

* See chapter on Amalgams. 



TIN. 121 

for these metals. The affinity of tin for gold in particu- 
lar has been clearly demonstrated by Dr. Matthiessen. 
Into a crucible of molten tin a rod of gold and one of 
copper were dipped, the latter having been previously 
tinned to ensure perfect contact. The gold united 
readily and rapidly with the tin, while the copper rod 
remained unaffected. A gold wire which has been super- 
ficially tinned will melt like one of tin when held in the 
flame of a Bunsen burner. A wire of tinned copper 
exposed to the same heat, under like circumstances, 
remains unaffected, except that the tin is burned off. 
The affinity of tin for platinum is so great, states Clarke, 
that if tin and platinum foils be rolled together and heated 
before the blow-pipe combination takes place explosively. 
The affinity of tin for gold is unquestionably an interest- 
ing subject for the dentist, in view of the place these two 
metals occupy in operative dentistry. 

Silver alloys with tin, and, in the proportion of 80 of 
the former to 20 of the latter, it is said produces a very 
tough alloy. 

Dr. G. F. Rees's alloy for artificial dentures, con- 
structed by the cheoplastic process, is composed of tin 
20, gold 1, and silver 2 parts. * Other alloys much used 
in cheoplastic work are composed largely of tin. 

Bean's alloy, intended for casting inferior dentures, 
is composed of tin 95, and silver 5 parts. 

Antimony 1 and tin 16 parts forms another alloy, 
which is intended for the same purpose, and was intro- 
duced by the late Dr. William B. Kingsbury. 

Brittannia metal is made under a great variety of for- 
mulae; one known as English is composed of antimony 
7.8, tin 90.7, and copper 1.5. It sometimes contains lead 
or bismuth. 

♦"Amalgams and Alloys Chemically Considered," by J. Morgan Howe, 
M. D., Transactions New York Odontological Society, 1880. 



122 



PRACTICAL DENTAL METALLURGY. 



Type metal, generally speaking, consists of lead, 
antimony and tin — lead 55, antimony 30, and tin 15 parts. 

Dr. L. P. Haskell's Babbitt metal for dies is com- 
posed of the following: "Copper 1 part, antimony 2 parts, 
tin 8 parts. These should be melted in the order named, 
as tin would oxidize badly before the first was melted, if 
all were placed in the crucible together. Melt, and turn 
off into ingots, and remelt. If it should not be found to 
run freely from the ladle, when making a die, add a small 
amount of tin, as it is presumable that some of that metal 
has oxidized."* 

Babbitt metal is made under a great variety of 
formulae; but one in the same proportions as the above 
(tin 12 paits, antimony 3 and copper 2 parts) is given by 
Dr. Kssig, which, he states, is sometimes used in the 
dental laboratory for dies, and is thought by many to be 
superior to zinc for that purpose, f 

Copper and tin form a large number of alloys of great 
importance. 

Bronze. — Copper and tin unite in almost any propor- 
tion to form bronze. 





Copper. 


Tin. 


Phosphorus. 


Zinc. 


U. S. Ordnance Bronze. 


90. 
90.34 

84.42 


10. 

8.90 
4.30 






Statuary Bronze 


0.76 




11.28 



Actual speculum-metal is supposed to have the 
formula, Cu 4 Sn, and the centesimal composition of 
copper 66.6 parts and tin 33.4 parts. 

Bell metal is copper 72 to 85 parts, and tin 15 to 26 
parts. 



* Dr. L. P. Haskell, 
f Dental Metallurgy. 



TIN. 123 

With iron, in the process of tin-plate manufacture, 
tin is said to alloy. 

Lead and tin alloy freely in all proportions, tin gener- 
ally imparting greater resistance to the lead. Such 
alloys constitute certain forms of pewter, an important 
class called "soft solders," and counter-dies.* 

TESTS FOR TIN IN SOLUTION.— To the sus- 
pected solution add a few drops of caustic potash or 
soda. A white precipitate is thrown down, soluble in 
excess of the reagent. 

Ammonia also gives a white precipitate /^soluble in 
excess of the reagent. 

Ammonium or hydrogen-sulphide throws down a 
brown, in the case of stannous, and yellowish-brown pre- 
cipitate with stannic chloride, both of which are soluble 
in excess of the reagent. 

Gold trichloride added to a dilute solution of the tin 
chlorides gives the characteristic purple precipitate, 
known as the purple of Cassius.f 

EXPERIMENT No. 25.— Test a tin-salt in solution as above. 

BLOW-PIPE ANALYSIS. — On charcoal, with 
sodium carbonate, tin is reduced to malleable lustrous 
globules. Under the O. F. these become incrusted with 
white stannic oxide. 

With Cobalt Solution. — Moisten the coal in front of 
the globules with the solution, and blow a strong R. F. 
upon the whole. The white oxide coat will become 
bluish-green when cold. 

In Borax Bead. — A faint blue bead is made reddish- 
brown or ruby-red by heating a moment with a tin com- 
pound in R. F. 

* See Lead Alloys, 
t See Gold. 



124 PRACTICAL DENTAL METALLURGY. 

INTERFERING ELEMENTS.— Alloys of Lead or 
Bismuth. It is a fair proof of tin if such alloy oxidizes 
rapidly with sprouting and cannot be kept fused. Zinc 
also interferes with the above tests. 

ELECTRO-DEPOSITION OF TIN.— Tin is easily 
deposited upon small articles of brass or copper by 
simple immersion, as by the following experiment: 

EXPERIMENT No. 26.— Place the articles in layers between sheets of 
grain tin in a saturated solution of potassium bitartrate and boil. A little 
stannous chloride may also be added, if necessary. 

The metal may be crystallized out of its solution and 
rendered pure by the following: 

EXPERIMENT No. 27.— Immerse a bar of tin in a strong solution of 
stannous chloride and pour on carefully, so as not to disturb the tin solution, 
some distillled water. Pure tin will be deposited on the bar of tin at the point 
of junction of the water and tin solution. 



CHAPTER IX. 

BISMUTH. 

Bismuthum. Symbol, Bi. 

Valence, III, V. Specific gravity, 9.82. 

Atomic weight, 207.52. Malleability, brittle. 

Melting point, 264° (507° F.). Tenacity, brittle. 

Ductility, brittle. Chief ore, native metal. 

Conductivity (heat), 1.8. Conductivity (electricity), 1.24. 

(Silver being 100.) 

Specific heat, 0.0308. Crystals, rhombohedral. 
Color, white with reddish tint. 

OCCURRENCE.— Practically the only ore of this ele- 
ment is the Native Metal found disseminated in veins 
through slate rock associated with the ores of copper, 
iron, cobalt, nickel, silver, gold, and arsenic. It also 
occurs as Bismuthine, or bismuth glance, a sulphide, 
Bi 2 S 3 , and the ore called Bismuth ochre, the trioxide, 
Bi 2 O s . It is a comparatively rare metal inasmuch as the 
supply has not kept pace with the demand, and its com- 
mercial value has risen considerably. It is found chiefly 
in Saxony, Transylvania, United States, England, Peru, 
Norway, and Sweden. 

REDUCTION.— This is simple and may be accom- 
plished by a process of sweating. The crushed ore is 
introduced into large iron tubes or tubular retorts, built 
in the furnace. These tubes are placed in an inclined 
position over a wood fire. At the upper end the ore is 
introduced, and as the metal is sweated out it accumu- 
lates at the lower end, where it is drawn off into iron 
vessels. The siliceous residue is then raked out of the 
tube at its upper end and the retort recharged. 

Commercial bismuth frequently contains arsenic and 
iron, besides gold and silver; hence is not fit for dental 



126 PRACTICAL DENTAL METALLURGY. 

usage until it is purified. When silver exists in bismuth 
in sufficient quantity to repay for extracting, it is cu- 
pelled just as lead is, during which the bismuth is oxi- 
dized, leaving the silver as a molten button on the cupel. 
The oxide of bismuth is afterwards recovered by strongly 
heating under powdered charcoal. At the same time the 
arsenic is gotten rid of, in that it volatilizes. The bis- 
muth is protected from oxidation by the covering of 
charcoal. The metal is also frequently fused with potas- 
sium nitrate, which removes the arsenic and iron by 
oxidizing them. To produce the pure metal, however, 
it is best to employ some humid method of refining, as: 

"EXPERIMENT No. 28.— Place a small amount of Bi. in a test-tube and 
add to it HNO s ; after the action of the acid has ceased, filter the solution 
into a beaker filled with distilled water. The bismuth will be precipitated 
as the subnitrate — BiONO s ; filter and wash first with a solution of caustic pot- 
ash, then distilled water, dry and heat in a crucible with about one-half its 
bulk of powdered charcoal — pure bismuth. 

PROPERTIES.— Bismuth is a highly crystalline, 
hard, and very brittle metal, having a grayish-white color, 
with a decided reddish tint. Its specific gravity is 9.823 
at 12° C* and fuses at 264° (507.2° F.). It expands 
about 1-32 of its volume upon cooling, and imparts this 
property to its alloys. It crystallizes in large, beautiful, 
iridescent rhombohedra, which near^ approach a cube, 
their angles being nearly 90°, (87°40'). These crystals 
may be obtained by melting a quantity of the metal and 
allowing the bulk to cool slowly, the surface being pre- 
vented from more rapid solidification by covering the pot 
with a sand bath filled with glowing coals. As soon as 
a crust has formed on the sides and top, it is pierced with 
a hot iron, and the still molten metal poured out. When 
quite cold the upper surface is sawed off, exposing the 
beautiful crystals in the interior. The metal volatilizes 

* Holzmann. 



BISMUTH. 127 



at a high temperature, and has a specific heat of 0.0308. 
It is the most diamagnetic of all substances. Exposed 
to the air at ordinary temperatures, it is unaffected, but 
when heated to a red heat it rapidly oxidizes, forming a 
play of beautiful colors. 

COMPOUNDS WITH OXYGEN.— Bismuth com- 
bines with oxygen to form two oxides: 

Bismuthous Oxide, the Trioxide^ Bi 2 3 , is found na- 
tive as bismuth ochre, and may be prepared by roasting 
the metal in air or by gently igniting its nitrate. It is a 
straw-yellow powder, insoluble in water; is fusible at a 
high temperature, and in that state acts toward siliceous 
matter as a flux. 

Bismuthic Oxide, the Pe?itoxide, Bi 2 O s , may be ob- 
tained by dissolving the trioxide in caustic potash and 
passing chlorine through the liquid; the water decom- 
poses, forming hydrochloric acid, and the trioxide is con- 
verted into the pentoxide. It is then washed with dilute 
nitric acid to separate any remaining trioxide. The 
pentoxide is a reddish-brown powder, which is insoluble 
in water. 

ACTION OF ACIDS ON BISMUTH.— Sulphuric 
acid when cold has but slight action on bismuth, but 
dissolves it more readily when heated, forming the sul- 
phate, and giving off sulphurous anhydride. 

Hydrochloric acid, hot or cold, but feebly attacks 
bismuth. 

Nitric acid dissolves bismuth very energetically, giv- 
ing off red fumes copiously and forming the nitrate or 
ternitrate, as it is generally termed, Bi3N0 3 , which is 
a white crystalline, soluble mass. 

If the ternitrate be added to a large quantity of water, 
a white precipitate is thrown down known as the sub- 
nitrate of bismuth, BiON0 3 , which is much used in 



128 PRACTICAL DENTAL METALLURGY. 

medicine and as pearl white or bla?ic de fard in cosmetics. 
It is a heavy white powder, insoluble in water or alcohol. 
It is darkened by sulphuretted hydrogen. 

ALLOYS. — Bismuth unites readily with other metals, 
the alloys being remarkable for their ready fusibility, 
and by their property of expanding on solidification. 
These two properties render it most valuable as an 
ingredient to alloys used for making casts or dies where 
it is essential to copy fine lines, and in alloys when a very 
low fusing point is desirable. 

With copper it forms a pale-red, brittle alloy. 

With zinc it easily unites, producing an alloy ll more 
brittle, presenting a larger crystallization with less 
adherence than zinc or bismuth taken singly."* It 
is, however, says Dr. Kirk, sometimes employed in the 
dental laboratory for the formation of dies, such an alloy 
having a lower fusing point than pure zinc, and being 
free from contraction on cooling. 

With tin bismuth alloys in any proportion. A very 
small quantity of the metal imparts to tin more hard- 
ness, sonorousness, luster, and a fusibility lower than 
either of the metals taken separately possesses. An 
alloy of equal parts of the two metals fuses at 212° C. 

With lead bismuth alloys very easily, producing an 
alloy which is malleable if the proportion of bis- 
muth does not exceed that of lead. The specific 
gravity is greater than the mean of the two taken sepa- 
rately. Its alloys are white, lustrous, harder than lead, 
and more malleablef up to a certain proportion. Bis- 
muth 1 and lead 2 gives a very ductile and malleable 
alloy fusing at 330° F. 

* William T. Brannt. 
t Ibid. 



BISMUTH. 



129 



With antimony it produces a grayish, brittle, lamellar 
alloy. Lead and tin added renders it malleable, but its 
fusibility is increased rather than decreased. Such 
alloys are very frequent and much used in the prepara- 
tion of Britannia and Queen's metal. 





Bi. 


Sb. 


Sn. 


Pb. 


Cliche-metal 


9. 

8. 
1. 


10.5 

Type-metal 

1. 

3. 


48. 
4. 


32.5 


1 1 


5. 


< < 


8. 









Alloys of bismuth, tin, and lead are known as the 
triple alloys, and are very numerous and useful. 

Newton's alloy consists of bismuth 8, lead 5, and tin 
3 parts, and fuses at 202° F. 

Rose's fusible alloy is composed of 

i. ii. 

Bismuth 2 8 parts. 

Tin 13" 

Lead 1 8 " 

The first fuses at 200.75° F. and the second at 174.2° F.* 
They were used as safety-plates and inserted in the top of 
steam boilers, intended to prevent the explosion of boilers 
by allowing the steam to escape at a certain tension. 

Wood's metal consists of lead 4, tin 2, bismuth 5 to 8 
and cadmium 1 to 2, melts at 140° to 161.5° F., in color 
resembles platinum, and is, to a certain extent, malleable. f 

Onion's fusible alloy contains lead 3, tin 2, and bis- 
muth 5 parts, and melts at 197° F. 

"La Nation" describes a new fusible alloy, of which 
the following is the formula: 

* William T. Brannt. 
f Ibid. 



130 



PRACTICAL DENTAL METALLURGY. 



Bismuth 48, cadmium 13, lead 19, and tin 26. It melts 
at 158° and resists great pressure. 

Hodgen's fusible alloy, for making dies and counter- 
dies by the dipping process, is composed of the following: 
Bismuth 8, lead 5, tin 3, and antimony 2. It is a light, 
lustrous alloy, very hard, slightly malleable, expands 
slightly on cooling, copying the finest of lines, takes a 
high polish and resists great pressure, melting at 224° F. 

Dr. Mathews Fusible Alloy. — This alloy is com- 
posed of bismuth 48, cadmium 13, and tin 19 parts. It 
melts below the boiling point of water and may be 
packed with the fingers. It may be poured into plaster 
impressions immediately after they have been taken, 
producing sharp, bright, hard dies, with which shot may 
be used for the counter- die. 

Darcet's fusible alloys are a series of proportions of 
bismuth, tin, and lead, and their melting point varies as 
per the following table : 



Parts. 


Melts. 


Bismuth. 


Tin. 


L,ead. 


7 
16 

8 


4 

7 
2 


2 
4 
6 


212°F. 
212 C F. 
205° F. 



Most of these fusible alloys are of much value in the 
dental laboratory in the hands of a practical, quick-witted 
man. The cleaner ones may, when lack of time will not 
permit of a more perfect repair, be used to mend a dentuie 
or replace a tooth or block of teeth on a vulcanite plate, 
and the more fusible ones may be used for the same pur- 
pose, even though the base be celluloid. In replacing 
teeth undercuts may be made with a file, or preferably 



BISMUTH. 131 



with a large bur in the engine, the tooth placed in posi- 
tion and the alloy packed in with warm instruments, 
smoothed and afterwards polished. These alloys are 
also valuable baths for tempering steel instruments. 
They give a very exact temperature, which may be 
adjusted to the purpose intended. They are used, 
according to Thurston,* by placing the articles on the 
surface of the unmelted alloy and gradually heating until 
fusion occurs and they fall below the surface, at which 
moment their temperature is right ; they are quickly 
removed and cooled in water. f "An alloy of 3 parts 
each bismuth, fine gold, and platinum with 15 of fine 
silver, and 10 of tin, is very similar to precipitated 
palladium, and has been used as a substitute for this 
costly metal. One curious point about this alloy is, 
asserts Mr. Fletcher, that if it contains the merest trace 
of palladium it is almost worthless; and as ordinary fine 
silver is rarely, if ever, free from palladium, this alloy 
can only be made from silver reduced direct from the 
chloride." 

In amalgams. — ' ' The addition of bismuth to amalgams 
makes them excessively sticky and adhesive, necessitat- 
ing, at the same time, an increase in the proportion of 
mercury required. "J 

The same author, continuing, says: " Amalgams con- 
taining a trace of bismuth will build and adhere to a flat 
dry surface, and may be used as a metallic cement for 
joints in apparatus which require to be perfectly air tight 
and to stand heavy pressures. A good alloy for this pur- 
pose is 1 bismuth, 15 tin, 15 silver, fused and filed up, 
and then mixed in the proportion of 1 alloy to 4 of mer- 

* Brasses, Bronzes, and other Alloys, p. 196. 

t Metallic Alloys, Brannt. 

t Dental Metallurgy, Thomas Fletcher, p. 65. 



132 PRACTICAL DENTAL METALLURGY. 

eury. This alloy is so excessively sticky as to be useless 
for fillings."* 

Commenting on the above, Dr. Kirk says:f " The effect 
of bismuth in dental-amalgam alloys does not seem to 
have been fully studied." And, further, "it would seem 
that the power of bismuth to overcome the contraction of 
alloys in solidifying would render it valuable as an in- 
gredient in certain dental-amalgam alloys if it conferred 
no objectionable qualities other than adhesiveness upon 
them." 

TESTS FOR BISMUTH IN SOLUTION.— Makins 
states: " The salts of this metal are for the most part 
devoid of color; some are soluble, others insoluble, the 
soluble salts redden litmus paper." 

Sulphuretted hydrogen or ammonium sulphide 
when added to a solution produce a black precipitate — 
sulphide of bismuth — insoluble in dilute acids or alkalis, 
but dissolves in strong hot nitric acid. 

The alkalis precipitate from bismuth solutions — in the 
absence of certain organic substances — the white bismuth 
hydrate, Bi3HO, insoluble in excess of the reagents, con- 
verted by boiling to the yellowish-white oxide, Bi 2 O s . 

The carbonates — as K 2 C0 3 — precipitate the white 
basic bismuth carbonate, Bi 2 2 C0 3 , insoluble in excess 
of the reagents. 

Water precipitates from acidulated bismuth solutions 
white basic salts, which contain less of their acid radicals 
in proportion as greater quantities of water are added, as — 

1st. Bi3N0 3 + 2H 2 0=BiON0 3 . H 2 + 2HN0 3 . 

2d. 4Bi3N0 3 + 6H a O=Bi 4 O s 2N0 3 . H 2 0+ 10HNO 3 . 

BLOW-PIPE AN ALYSIS.— On charcoal with sodium 
carbonate, before the blow-pipe, bismuth is easily reduced 

* Dental Metallurgy, Thomas Fletcher, p. 65. 
t American System of Dentistry, Vol. Ill, p. 931. 



BISMUTH. 133 



from all of its compounds. The globule is easily fusible, 
brittle (which fact distinguishes it from lead), and is 
gradually oxidizable under the flame, forming an incrus- 
tation — Bi 2 3 — orange yellow while hot, and pale yellow 
when cold. 

In borax bead it gives a faint yellowish color when hot, 
and is colorless when cold. 

ELECTRO-DEPOSITION OF BISMUTH.— This 
metal may be deposited by simple immersion or by means 
of an extremely feeble current; in the former case zinc, 
tin, lead, and iron deposit bismuth upon themselves. 



CHAPTER X. 

ZINC. 

Zincum. Symbol, Zn. 

Valence II. Specific gravity, 6.915. 

Atomic weight, 64.9. Malleability, 8th rank. 

Melting point, 415° (779° F.). Tenacity, 6th rank. 

Ductility, 6th rank. Chief ore, Calamine. 

Specific heat, 0.0956. Crystals, rhombohedral. 
Color, bluish-white. 

OCCURRENCE.— Zinc is a somewhat abundant 
metal, but never occurring in the native state. It is found 
as a carbonate, sulphide, silicate, etc, associated with 
lead ores in many districts; large supplies are obtained 
from Silesia and from the neighborhood of Aachen. 

The native carbonate, (1) Calamine, Smithsonite, 
ZnC0 3 , is the most important of its ores. Asa rule this 
ore is a light-gray, yellow, or buff in color, having a 
specific gravity of 4 to 4.5. (2) Zinc-Blend, the sulphide, 
ZnS, is second in importance only to the above; it is ex- 
tensively mined, and much of the zinc of commerce is 
procured from this ore. Its color is green, yellow, or 
red, but mostly brown, having a specific gravity of 
3.9 to 4.2. There is also a (3) Red Zinc Ore, an impure 
oxide, ZnO; an (4) Electric Calamine, one of the silicates, 
ZnO.Si0 2 + H 2 and (5) Willemite, an anhydrous sili- 
cate, ZnO.Si0 2 . 

REDUCTION.— -Calamine, ZnC0 3 ,is generally reduced 
by first roasting, to expel the water and carbon dioxide. 
This leaves the oxide, ZnO, which is then mixed with 
fragments of coke or charcoal, and distilled at a full red 
heat in a large earthen retort. The carbon unites with 
the oxygen to form carbon monoxide and escapes, while 
the reduced metal volatilizes and is condensed by suitable 



zinc. 135 

means, generally contaminated with minute quantities 
of arsenic. Zinc-blend is roasted to drive off the sulphur, 
but when it contains any foreign sulphide, as of lead, it 
is more difficult, and requires some twelve hours' roasting. 

EXPERIMENT No. 29.— Melt old, partially oxidized zinc in a crucible, 
and when molten, cover the surface with pulverized charcoal; heat at a strong 
temperature, and stir with a stick of wood. After a few minutes the zinc 
may be poured, and will be found to be quite free of the oxide. 

Thus old zinc may be refined or cleaned for use again 
in the laboratory. 

PROPERTIES.— Zinc is a bluish-white metal, which 
but slowly tarnishes in moist air, usually forming a super- 
ficial carbonate; it has a lamellar, crystalline structure, 
a specific gravity of 6.915, and is, under ordinary circum- 
stances, quite brittle, but when heated to 100° or 150° C. 
it may be rolled or hammered into thin sheets, or drawn 
into wire; and, what is very remarkable after such treat- 
ment, it retains its malleability when cold; the sheet zinc 
of commerce is thus made. If the temperature be carried 
to 205° C. it again becomes so brittle that it may be 
easily powdered in a mortar. Care should be exercised 
in handling hot zinc dies, for if by accident one be dropped 
upon a hard surface it is likely to be ruined. The metal 
melts at 415° C. or 779° F. It boils and volatilizes at 
1040° C. or 1904° F., and, if air be admitted, burns with 
a splendid greenish incandescence, forming the oxide. In 
boiling water zinc is said to be attacked appreciably, but 
no more, forming the hydroxide, Zn2HO, with evolu- 
tion of hydrogen. 

EXPERIMENT No. 30.— Test zinc for malleability at ordinary temper- 
atures; when heated to from 100° to 150° C; and also at 205° C. 

IN THE ARTS. — Zinc meets with extensive applica- 
tion. It is much used for the positive element in galvanic 
batteries, and in the form of sheet zinc it is greatly 
employed in manufacturing industries. 



136 PRACTICAL DENTAL METALLURGY. 

DENTAL APPLICATIONS.— Zinc has long been 
very extensively used in the dental laboratory for making 
dies. Its comparatively low fusibility, hardness, and other 
properties eminently fit it for this purpose. 

DIES. — " In passing from a low to a higher tempera- 
ture zinc increases in volume in a greater ratio than 
any of the metals in common use. The coefficient of 
its cubical expansion between zero and 100° C, 
which represents the rate of increase of its unit volume 
between these temperatures, has been found to be 
0.000088251, or nearly three times that of cast iron. 
The rate of expansion of liquids being greater than that 
of solids, and as this rate is not constant, but increases 
with the temperature, the rate of increase in volume 
which zinc undergoes in passing from the solid to the 
fluid condition would be represented by a figure some- 
what higher than that given above. From the fact that 
metal plates for entire dentures which have been swaged 
upon dies made of zinc generally fail to fit the plaster 
model accurately, it is held by some practitioners that 
the high rate of expansibility of zinc is an undesirable 
feature; but as the absolute contraction in the size of a 
zinc die is but slight, and as the difference in the size of 
a plate made upon it and that of the mouth for which it 
is intended is to a certain extent reduced or counteracted 
by the expansion which the plaster model undergoes in 
setting, it is questionable whether the contraction which 
takes places in zinc on passing from the fluid to the solid 
condition is of any detriment. It is held by many, and 
for potent reasons, that in most cases the contraction 
which occurs in a zinc die is of positive benefit. A plate 
swaged upon a zinc die is, by reason of the contraction 
which the metal undergoes in passing from the fluid to 
the solid state, slightly smallet than the mouth it is 
intended to fit, thus bringing the greatest pressure to bear 
upon the alveolar ridge. Should the plate be made to fit 
upon the plaster cast, it would be a trifle larger than the 
mouth, as plaster expands in setting, and two expan- 
sions have taken place in taking the impression and 
making the cast. The pressure exerted by such a plate 



zinc. 137 

would be expended upon the bony arch of the hard 
palate. Usually, the tissues covering the alveolar ridge 
are thicker, and therefore more yielding, than those 
covering the hard palate, and a plate swaged upon a zinc 
die would be of positive advantage, as the slight absorp- 
tion of the tissues covering the alveolar ridge which 
result from the increased pressure would soon bring 
about a perfectly uniform bearing over the entire area 
covered by the plate. But one class of cases arises, and 
their occurrence is infrequent, where the quality of ex- 
pansibility of zinc is detrimental to the fit of a plate when 
swaged upon it — namely, where the tissue covering the 
bony arch of the hard palate are thick and spongy, while 
the alveolar ridge is hard and covered by a thin un- 
yielding membrane. When this set of conditions pre- 
sents, it is usually in combination with a high V-shaped 
arch. In such cases a die of Babbitt metal gives better 
results, though even with a zinc die the difficult}' can be 
readily overcome and a proper adaptation secured by 
properly manipulating the plaster cast or impression, 
i. e., by scraping those portions of the cast which repre- 
sent the soft, yielding portions, or by treating the im- 
pression in like manner at those positions which represent 
the hard or unyielding parts of the ridge. "* 

Counter-Dies. — Zinc is frequently used for making 
the counter-die as well ; being hard and unyielding, 
copying the finest lines, it secures a perfect and ready 
adaptation of the metal to the die. In working platinum- 
gold or iridium-platinurn the lead die is entirely inade- 
quate to perfectly swage the metal to the die, especially 
where the palatine arch is very high or the rugae promi- 
nent, and it is then that a zinc counter-die is especially 
serviceable. It is also of great assistance in conforming 
plates to dies for partial dentures, as it more perfectly 
forces the metal snugly about the necks of the teeth than 
lead can be made to do. 

* Dr. E. C. Kirk, Am. System of Dentistry, Vol. Ill, p. 922. 



138 PRACTICAL DENTAL METALLURGY. 

The zinc counter is formed similarly to the manner of 
making a lead counter, except that the die should be 
quite cool* — not cold — and thinly coated with a solution 
of whiting", which is allowed to dry, or with a deposit of 
carbon, obtained by smoking the die over a candle flame. 
In experienced hands the coating may be dispensed with 
and zinc heated just to complete fusion , and quickly poured 
in a?i uni?iterrupted stream upon the cool die. 

Dr. Essigf recommends, where swaging is likely to 
be attended with difficulty, "at least three sets of dies 
and counter-dies. " For the most imperfect of these he 
pours a lead counter-die and uses it for the preliminary 
swaging of the metal to the die. A partial lead counter 
is also exceedingly serviceable in the preliminary con- 
formation of the plate to the buccal and labial portions of 
the process. Such a counter is held in position by vari- 
ous means, the most practical of which, that has come 
to the writer's notice, is one used by Dr. Thomas N. 
Iglehart, consisting of a large steel screw-clamp, the 
bow of which may be represented by the letter U laid 
on one side, thus p. The end of the lower side termi- 
nates in a large circular section of iron, provided with a flat 
base, perforated for screwing into the bench. The upper 
arm carries a screw, similar to those used in letter presses, 
and when the die is placed on the heavy iron below the 
screw centers the partial counter from above, thus hold- 
ing the two in a perfect grip, permitting swaging with 
the hammer or tracer all around. Such a device is 
especially serviceable in turning the rim. A second die 
is furnished with a zinc counter, and when the plate is 

* If melted zinc is poured at 800° F. upon a zinc die at 70° F., the fused zinc 
by contact with the iron ring and by radiation will lose heat enough to cause 
its temperature to fall far below the fusing-point, and it will probably not 
impart to the die more than 400° F. — Essig. 

t Dental Metallurgy, p. 232. 



zinc. 139 

so far conformed to the shape of the die as to preclude 
all probable wrinkling or folding, this counter is adjusted 
and the plate more perfectly driven to the die and the 
finer lines accurately copied. As the die is necessarily 
much marred by the unyielding quality of the counter, a 
third and very perfect die provided with a lead counter 
should be used to complete the swaging. The writer 
prefers to put the counter-die down finally under a steady 
pressure of from 1000 to 5000 pounds by means of a screw 
press. 

THE COMPOUND WITH OXYGEN.— Zinc oxide, 
ZnO, is the only known compound of this metal and 
oxygen. It is a strong base, forming salts isomorphous 
with those of magnesium. It may be prepared by the 
combustion of the metal, heating it to 1900° F., exposed 
to the action of the atmosphere. Soon alter melting it 
begins to be covered with a film of gray oxide. When 
the temperature nearly reaches redness it takes fire and 
burns with an intense white light, generating the oxide 
in the form of very light and white flocculi, resembling 
carded wool, which quickly fill the crucible, and are in 
part driven into the atmosphere by the current of air. It 
may also be prepared by heating the carbonate, ZnC0 3 , 
to redness, driving off the water and carbon dioxide, C0 2 . 
Too high a temperature will discolor the oxide a light 
yellow, and, partially vitrifying it, will give to it a harsh, 
gritty feel. A good quality should present a soft, white, 
flaky, impalpable powder, permanent in air, odorless and 
tasteless, insoluble in water or alcohol, but soluble in 
acids without effervescence. When strongly heated the 
oxide assumes a deep lemon color, but turns nearly white 
again on cooling. At a low white heat it fuses, and at 
a full whiteness sublimes. If it be contaminated with 
white lead or chalk, it will not be entirely soluble in 



140 PRACTICAL DENTAL METALLURGY. 

dilute sulphuric acid, but an insoluble sulphate of lead 
or of lime will remain. If not properly calcined, and 
any carbonate remains, it may be detected by treating 
with hydrochloric acid, causing effervescence. In medi- 
cine it is used as a tonic, astringent, and applied ex- 
ternally as an ointment. As a cosmetic it has a great 
advantage over lead in not being poisonous. It is also 
used as a substitute for white lead in paints, and has the 
advantage of not being discolored by sulphuretted 
hydrogen. 

BASIC ZINC CEMENTS.— The basic zinc cements 
used in deutistry are the phosphate, the oxychloride, and 
the oxysulphate. 

The powder is prepared by calcining a quantity of 
the purest zinc oxide, luted in a sand or French clay 
crucible, for several hours, at a white heat. 

Every precaution should be taken to obtain pure oxide, 
and each specimen should be carefully tested before cal- 
cining. The commercial metallic zinc, of which most of 
the oxide is made, contains, among several other impur- 
ities, arsenic. So that arsenic compounds are apt to be 
contained in cheap qualities of oxide of zinc. Dr. Kirk 
recommends Hubbuck's English as a preparation most 
likely to be reliable. 

EXPERIMENT No. 31 A.— Into a test-tube half filled with water place 
eight or ten grains of pure zinc oxide and boil, add a few drops of hydrochloric 
acid, and then a small quantity of a solution of sulphuretted hydrogen. Note 
no precipitate appears. 

EXPERIMENT No. 31B.— Into a test-tube half filled with water place 
eight or ten grains of zinc oxide, to which has been added one grain of 
arsenious oxide, boil, add a few drops of hydrochloric acid, and then a small 
quantity of a solution of sulphuretted hydrogen. Note that the experiment is 
distinguished from No. 31A by the formation of a lemon-yellow precipitate, 
the sulphide of arsenic. This is a test for the presence of arsenic, and may 
be used in testing the oxide of zinc. 



ZINC. 141 

After the oxide has been properly calcined it is found 
to be greatly contracted in mass, semi-vitrious, and light 
yellow in color. 

When cool it is removed from the crucible, broken up 
and ground to a fine powder between mill-stones. The 
powder is bolted through a fine bolting cloth, and then 
placed in tightly stopped bottles ready for use. The 
bottles are tightly corked, for if exposed to the air the 
oxide absorbs carbon dioxide and a portion of it is con- 
verted to carbonate of zinc. Other oxides are frequently 
mixed with the oxide of zinc, such as the oxides of 
aluminum, magnesium, and tin, with a view to improving 
its properties. The native oxide of titanium, powdered 
rutile, slate, etc., are frequently used to give it a 
variety of shades to meet the demand. Ground glass, 
silica, borax, etc., are sometimes added to improve its 
wearing qualities. Their value is questionable. 

The Liquid. — For the phosphate cements the liquid is 
usually made by dissolving glacial (metaphosphoric) 
acid, HP0 3 , in distilled water and evaporating to a 
syrupy consistence. The commercial acid contains such 
impurities as sodium and magnesium phosphates in vari- 
able amounts, and since these impurities, like the acid 
itself, are soluble in water, but form no chemical com- 
bination with zinc oxide, they remain in the cement to 
be dissolved out by the saliva. 

After standing they sometimes recrystallize, owing to 
a lack of water. When this tendency is noticed, a drop 
or more of water should be added. They also sometimes 
become turbid or cloudy after a few days or weeks stand- 
ing, showing deterioration. 

The liquid for the oxychloride is prepared by deliques- 
cing half an ounce of crystalline chloride of zinc with 
two or three drams of distilled water. Some heat is 



142 PRACTICAL DENTAL METALLURGY. 

generated during the process; therefore, the bottle con- 
taining it should not be too tightly stopped. Any residue 
should be allowed several days to settle, when the clear 
supernatant liquid is decanted off for use. 

Mixing. — The prepared oxide of zinc is mixed on a 
slab with enough of the liquid to make a semi-thick, 
plastic, putty-like mass, when it is ready for introduction. 

The deliquesced chloride and prepared zinc oxide are 
mixed to form the oxychloride, but the paste should 
not be worked as stiff as the phosphate. It is best 
mixed to a thick, creamy consistence, and immediately 
introduced. 

EXPERIMENT No. 32.— Each student should prepare a small quantity 
of oxide by heating metallic zinc to about 1900° F. in an uncovered crucible. 

EXPERIMENT No. 33.— Calcine at a white heat for two hours a small 
quantity of oxide of zinc; powder in a mortar, and pass through a fine sieve. 

EXPERIMENT No. 34.— Prepare a small quantity of glacial phosphoric 
acid solution, as previously described. 

EXPERIMENT No. 35.— Prepare a small quantity of chloride of zinc 
solution, as previously described. 

Oxysulphate. — What is known as the oxysulphate of 
zinc to dentists, is merely a mixture of oxychloride of 
zinc and zinc sulphate. A true zinc oxysulphate is pre- 
pared by saturating a solution of zinc sulphate with zinc 
oxide. It forms a white paste, sets quickly, and attains 
about the same hardness as plaster of Paris. It is prin- 
cipally used as a capping for exposed pulps. It is bland 
and non-irritating, a non-conductor, and faintly and per- 
sistently astringent. 

ACTION OF ACIDS ON ZINC— Pure zinc dis- 
solves very slowly in acids (or alkalis), unless in contact 
with copper, platinum, or some less positive metal. Any 
metallic impurity in zinc renders it quite soluble in the 
acids or (alkalis). It is rapidly oxidized in water con- 



ZINC. 14o 

taitiing air, when in contact with iron, but the water does 
not dissolve it, unless aided by certain salts. All agents 
which dissolve the metal, also dissolve its oxide and 
hydroxide. 

In Sulphuric acid dilute, it dissolves slowly, forming 
zinc sulphate, and evolving hydrogen — 
Zn+H 2 S0 4 =ZnS0 4 +H 2 . 

In strong sulphuric a coating of zinc sulphate is quickly 
formed over the metal, retarding, if not altogether pre- 
venting, further solution. 

In Hydrochloric acid it is also slowly dissolved when 
pure, more rapidly when contaminated, forming the 
chloride of zinc and evolving hydrogen — 
Zn + 2HCl=ZnCl 2 + H 2 . 

The Chloride is a nearly white, translucent, fusible 
substance, very soluble in water and alcohol, and very 
deliquescent. It is used in dentistry when melted, or 
melted and diluted as liquid for oxy chloride cements; 
as an obtundent to sensitive dentine, an antiseptic, dis- 
infectant, etc. 

In Acetic acid zinc slowly dissolves, forming the 
acetate, and evolving hydrogen — 

Zn + 2HC 2 H 3 0=Zn (C 2 H 3 2 ) 2 + H 2 . 

In Nitric Acid. — In very dilute nitric acid it dis- 
solves without evolution of gas — 

4Zn+ 10HNO 3 =4Zn(NO 3 ) 2 + H 4 NN0 3 + 3U 2 0, 
forming the nitrates of ammonium and zinc. 

In moderately dilute cold nitric acid, it dissolves with 
evolution of nitrous oxide — 

4Zn+10HNO 3 =4Zn(NO 3 ) 2 + N 2 O + 5H 2 O. 

In a less dilution it dissolves with evolution of nitric 
oxide — 

3Zn + 8HN0 3 =3Zn(N0 3 ) a + 2NO + 4H 2 0. 



144 PRACTICAL DENTAL METALLURGY. 

In concentrated nitric acid zinc is but slightly soluble. 

IN ALKALIS. — In Potassium Hydrate, and in all 
the caustic alkalis, zinc slowly dissolves, evolving 
hydrogen — 

Zn+2KHO=K 2 OZnO+H 2 . 

EXPERIMENT No. 36.— In each of five test-tubes place a small piece 
of zinc, and add respectively sulphuric (dilute), hydrochloric, acetic, and 
nitric (dilute) acids, and a strong solution of potassium hydrate, and note 
the action. 

ALLOYS. — Mercury and zinc amalgamate quite 
readily to form a definite compound, having the formula 
Zn 2 Hg.* 

With Gold, zinc readily unites. The malleability, 
brilliancy, and color of gold is impaired by a content of 
zinc. 

Platinum. — Small pieces of platinum may be dissolved 
in molten zinc, and the union is attended with consid- 
erable energy, owing to the formation of a definite chemi- 
cal compound. The alloy is hard and brittle. An alloy 
may be prepared of platinum, 16; copper, 7; and zinc, 1; 
which very much resembled gold in color, specific 
gravity, and ductility. 

Silver and zinc have a great affinity for each other. 
This fact, with the knowledge that zinc and lead are so 
comparatively incompatible, led to the process of desil- 
vering lead by the assistance of zinc. The alloy of silver 
and zinc is best obtained by throwing the required quan- 
tity of zinc wrapped in paper into, molten silver, stirring 
thoroughly with an iron rod, and pouring the fused 
mass at once. The alloy of two parts zinc and one part 
silver is flexible, ductile, and has nearly the color of 
pure silver. Larger proportions of zinc produce brittle 
alloys. 

* See chapter on Amalgams. 



zinc. 145 

Copper and Zinc Alloys. — (See chapter on Copper.) 

Iron and zinc unite to form a very interesting as well 
as somewhat useful and brittle alloy. On account of its 
brilliant light it may become of considerable value in 
pyrotechnics. It is best prepared by heating zinc in a 
crucible and adding anhydrous sodium ferrous chloride 
upon the surface of molten zinc, immediately covering 
the crucible. An energetic reaction takes place during 
the union. 

Iron plate and ware when perfectly cleaned may be 
immersed in molten zinc and the surface alloyed slightly, 
forming what is known as "galvanized iron," the name 
being derived from the circumstance that the coating is 
analogous to that produced by electrical means. Zinc 
alloys with the iron melting-pots of the laboratory; the 
admixture rendering the zinc less fluid when molten and 
more difficult to fuse. This contamination may be pre- 
vented by coating the pot with whiting. 

With Lead zinc does not alloy, except to a very slight 
degree. ' ' Matthiessen found* that on melting equal 
parts of zinc and lead, and, after well mixing, allowing 
the alloy to cool slowly, they separate, but the heavier 
lead on subsiding retains 1.6 per cent, of the zinc alloyed 
with it; while on the other hand the upper layer of zinc 
thrown out retains 1.2 per cent, of lead." 

It often occurs that lead and zinc will become mixed 
in the laboratory, and is seldom discovered until the 
molten mixture is poured. Then the lead, owing to its 
greater specific gravity, falls to the bottom of the mold, 
forming the alveolar ridge of the die, rendering it worth- 
less. Many times the counter-die is poured before the 
mistake is noticed, resulting in a union of the die and 
counter-die. 

*Makins' Metallurgy, p. 62. 



146 PRACTICAL DENTAL METALLURGY. 

Tin and zinc alloy in almost any proportion. Mr. 
Fletcher* recommends an alloy of zinc 2 parts and tin 
1 part for making dies for swaging, claiming the impres- 
sion from the sand is much finer, and the shrinkage on 
cooling is greatly reduced. It melts much lower than 
zinc alone, hence some care must be exercised in pouring 
the counter-die. The die should be perfectly cold and 
the lead should be just hot enough to pour, but not 
sufficiently heated to char a slip of paper. 

EXPERIMENT No. 37.— Form an amalgam of zinc. 

EXPERIMENT No. 38.— Melt 1 ounce of zinc with 1 ounce of lead; cast 
in a long ingot and notice separation. 

EXPERIMENT No. 39.— Make sufficient alloy of zinc 2 or 3 parts and 
tin 1 part to form a small die, and mold. 

EXPERIMENT No. 40.— Form an alloy of zinc and copper (brass) in 
any proportion. (Best to melt in separate crucibles and pour together while 
molten.) 

TEST FOR ZINC IN SOLUTION.— The Caustic 
Alkalis all precipitate the white hydroxide of zinc, 
Zn2H0, soluble in excess of either precipitant with the 
formation of sodium zinc oxide, etc. 

ZnCl 2 +2NaHO=Zn2HO+2NaCl. 
Zn2H04-2NaHO=Na 2 OZnO+2H 2 0. 

Ammonium sulphide completely precipitates zinc as 
a sulphide. 

Alkaline carbonates precipitate it as basic carbonate 
soluble in ammonia. 

EXPERIMENT No. 41.— Add to a solution of any of the zinc salts 
(ZnS0 4 ) in a test-tube a few drops of— 

a. Caustic potassa: white precipitate, soluble in excess; 

b. Caustic soda: " " " " " 

c. Ammonia: " " " " " 

d. Ammonium sulphide: " " (if pure) insoluble 

in excess. 

* Dental Metallurgy, p. 69. 



zinc. 147 

BLOW-PIPE ANALYSIS.— On Charcoal with 
Sodium Carbonate before the blow-pipe compounds of 
zinc are reduced to metallic zinc. 

The metal on charcoal is easily oxidized: film yellow 
when hot and white when cold. 

With Cobalt Solution. — Moisten the coal in front of 
the lead with a drop or so of solution of cobalt nitrate 
and blow a strong reducing flame upon the partially 
oxidized bead. The coal will be a bright yellow-green 
when cold. 

INTERFERING ELEMENTS.— If the zinc is not 
pure, the interfering elements are a?iiimony, cadmium, 
lead, bismuth, or tin. Cadmium, lead, or bismuth will 
not prevent the cobalt solution test, however. 

EXPERIMENT No. 43.— Heat a small piece of zinc on charcoal with 
the O. F., and notice the yellow oxide in front of the assay, which turns white 
when cold. 

EXPERIMENT No. 43.— Moisten the coal in front of the assay with 
cobalt solution, and heat in R. F., and the oxide will have a bright yellow- 
green color. 

ELECTRO-DEPOSITION OF ZINC— This metal 
is too electropositive to be readily set free by simple 
immersioo, except by means of metals more electroposi- 
tive than itself, such as magnesium. It is best deposited 
by means of a separate current, preferably from the sul- 
phate solution, using a large zinc anode, yielding a very 
good deposit from two small cells feebly charged. 

Iron was formerly so coated to protect it from rusting, 
arid called "galvanized iron." It is not so coated at 
present. 



CHAPTER XI. 

CADMIUM. 

Cadmium. Symbol, Cd. 

Valence, II. Specific gravity, 8.54. 

Atomic weight, 111.83. Malleability, 5th rank. 
Melting point, 320° (608° F. ). Ductility, 11th rank. 

Tenacity, 10th rank. Chief ore, Greenockite. 

Specific heat, 0.0567. Crystals, octahedral. 
Color, tin-white. 

OCCURRENCE.— This metal does not occur native. 
There is but one mineral known which could be called 
an ore of cadmium, and which contains it in any quan- 
tity; namely, the sulphide, CdS, greenockite, which is 
found near Bishopstown, Renfrewshire. This ore is 
crystalline, belonging to the hexagonal system, and is of 
an orange-yellow color. Cadmium is, however, often 
associated with zinc-blende, ZnS, and Calamine ZnC0 3 , 
and from these two ores it is principally obtained, vary- 
ing in amount from 1 to 5 per cent. The metal very 
much resembles zinc, especially in its chemical properties. 

REDUCTION.— A humid method (Stromeyer's) is 
to dissolve the zinc ore containing cadmium in dilute 
sulphuric acid and precipitate the metal as the orange- 
yellow sulphide by means of sulphuretted hydrogen. 
The sulphide is then dissolved in hydrochloric acid, the 
excess of the solvent evaporated, and the cadmium 
thrown down as the carbonate by adding ammonium 
carbonate. By heating this to redness the carbon dioxide 
is driven off, leaving the oxide, which is mixed with 
carbon and distilled from an earthen retort. 

PROPERTIES.— Cadmium is a tin-white, lustrous 
metal, tough, very volatile (next to mercury), and some- 
what harder than tin, which it very much resembles 



CADMIUM. 149 



physically. It fuses at 320° (608° F.)* and boils at 
860° C.,f giving off a yellowish-brown colored vapor. 
Its specific heat is 0.05669J; electric conductivity some- 
what lower than that of zinc and its specific gravity 8.546 
(ingot) and 8.667 (hammered). § It is malleable, ductile, 
and somewhat tenacious, breaking under an increasing 
strain, with fibrous scaly fracture; may be readily crys- 
tallized in regular octahedra; is unalterable in the air at 
ordinary temperatures, but when heated strongly in the 
presence of air, burns, emitting the yellowish brown 
fumes of cadmium oxide, CdO. 

COMPOUNDS WITH OXYGEN.— Cadmium forms 
a single oxide, CdO, a yellowish-brown powder, which 
is easily volatilized, or may be readily reduced with 
hydrogen or carbon, at a high temperature, but below 
that point necessary for the reduction or volatilization of 
zinc oxide. It is strongly basic and forms a series of 
salts similar in constitution to those formed by the oxide 
of zinc. It may be formed by burning the metal in the 
air, or by calcining the nitrate or carbonate, differing 
somewhat in shade according to the manner of prepara- 
tion. 

ACTION OF ACIDS ON CADMIUM.— In hot 
sulphuric or hydrochloric acid, moderately diluted, it 
is slowly dissolved, forming the salts CdS0 4 or CdCl 2 , 
and liberating hydrogen. 

In Nitric acid it is readily soluble, forming the 
nitrate, and generating nitrogen oxides. 

COMPOUNDS OF CADMIUM.— The most impor- 
tant of these is the sulphate, CdS0 4 , which is used in 
medicine as an astringent and stimulating remedy, 

* Rudberg. 

f Deville and Troost. 

X Regnault. 

\ Schroder. 



150 PRACTICAL DENTAL METALLURGY. 

especially in diseases of the eye. The next of impor- 
tance is the sulphide, CdS, which occurs native as green- 
ockite, and is used as a superior yellow pigment by 
artists. The iodide, Cdl 2 , is used in photography. 
There is also a chloride, CdCl 2 . 

ALLOYS. — The metal is of little use except as a 
constituent of certain alloys, especially those fusing at a 
low temperature. 

With mercury cadmium combines readily to form a 
silver-white mass, which readily crystallizes, and under 
certain circumstances is said to be malleable. When in- 
troduced into a dental-amalgam alloy, it imparts the 
property of malleability. Such dental alloys, however, 
cannot be too strongly condemned. 

" In 1848, Dr. Thomas W. Evans of Paris introduced 
his amalgam, which was composed of pure tin, cad- 
mium, and mercury; but it was soon found that cad- 
mium was one of the very worst metals that could be 
used in a dental alloy, and its use was soon discon- 
tinued."* 

Of it Dr. J. Foster Flagg, Philadelphia, says: " The 
promises of this alloy were certainly alluring. It was 
easily amalgamated; the amalgam was readily inserted; 
it did not discolor; it 'set' with surprising celerity; it 
made a sufficiently resisting filling. What wonder, then, 
that the gentleman who introduced it was pleased with 
the material? * * * My satisfaction was, however, 
very short-lived, for only three or four months passed 
before sundry indications presented, which aroused my 
suspicions as to the uniform integrity and durability of 
the material — these were, an occasional, but evident 
crevicing at edges; a gradual softening and disintegra- 

* Relative Merits of Filling-materials, by E. T. Darby, M. D., D. D. S. 
Dental Cosmos, Vol. XXXVI, p. 178. 



CADMIUM. 



151 



tion of some fillings; and the yellowish discoloration 
sometimes apparent in adjoining tooth structure." He 
further states that in some cases the " dentine had be- 
come thoroughly decalcified, and stained to a bright 
orange-yellow color — sulphide of cadmium." He ex- 
plains that pulps under such fillings were " devitalized," 
except " where thick septa of dentine existed between the 
bottoms of the cavities of decay and the pulp cavities."* 

" Cadmium shares with bismuth the property of 
strongly reducing the melting points of alloys, there 
being some whose melting point is so low that they can 
be liquefied in hot water. But while bismuth alloys are 
nearly all brittle, many alloys of cadmium possess con- 
siderable ductility, and can be worked under the hammer 
as well as between rolls. They act, however, very differ- 
ently in this respect, there being alloys which are ductile, 
and others again, though containing besides cadmium the 
same metals, only in different proportions, which are 
very brittle, "f 

These alloys are usually made up of cadmium, tin, lead, 
bismuth, and sometimes mercury, the latter being added 
chiefly to lower the melting point still more. The follow- 
ing are a few cadmium alloys with their melting points. 



J Alloy. 



L,ipowitz's Alloy. . . 

Wood's Metal 

Other Alloys, No. 1 
a 2 

»< 1 ( << o 

<i n <« 4 

£< a << 5 

Cliche Metal 



Cadmium. 


Bismuth. 


Tin. 


I,ead. 


3 


15 


4 


8 


1 to 2 


5 to 8 


2 


4 


2 


16 


3 


11 


10 


8 


3 


8 


1 


4 


1 


2 


1 


7 




6 


1 


3 


2 




22)4 




36 


50 



Fuses at 



158° F. 
140° to 161° F. 
170° F. 
167° F. 
150° F, 
179.5° F. 
203° F. 



^Plastics and Plastic Fillings, p, 54, First Edition. 

t Metallic Alloys, Brannt, p. 297. 

J Formulae and fusing points from Brannt. 



152 PRACTICAL DENTAL METALLURGY. 

TESTS FOR CADMIUM IN SOLUTION.— Sul- 
phuretted hydrogen throws down the orange-yellow 
sulphide, CdS, from acid solutions, distinguishing the 
metal from zinc. 

The Caustic Alkalis precipitate the white hydrated 
oxide, Cd2HO, soluble in excess of ammonia, but insol- 
uble in potassa or soda. 

On charcoal before the blow-pipe, with sodium car- 
bonate, cadmium is reduced to metallic salt, and usually 
vaporized and reoxidized nearly as fast as reduced, form- 
ing the characteristic yellowish-brown incrustation of 
oxide, CdO. 

To borax bead it gives a yellowish color while hot, 
colorless when cold. 

ELECTRO-DEPOSITION OF CADMIUM.— This 
may be accomplished by contact with gold or copper 
in a boiling solution of cadmium sulphate, when thin, 
white, brilliant and adherent cadmium is deposited upon 
the gold or copper. It may also be deposited in a regu- 
line state by a separate current. 



CHAPTER XII. 
COPPER. 

Cuprum. Symbol, Cu. 

Valence, II, (Cu 3 ) II. Specific gravity, 8.94. 

Atomic weight, 63.17. Malleability, 3d rank. 

Melting point, 1200° (2192° P.). Tenacity, 2d rank. 

Ductility, 5th rank. Chief ore, copper pyrites. 

Conductivity (heat), 73 6. Conductivity (electricity), 99.95. 

(Silver being 100.) 

Specific heat, 0.0952. Crystals, isometric. 
Color, red. 

OCCURRENCE.— This exceedingly interesting and 
useful metal has been known and used by the human 
race since the most remote periods. Its alloy of tin-bronze 
was the first metallic compound used by man. It is 
found in the metallic state, in masses of irregular form, in 
rocky fissures; and often crystallized in the Lake 
Superior region, and in Virginia, the southwestern portion 
of the United States, in Mexico, Chile, Cornwall, and 
many other parts of the world. Native copper is 
obtained in pieces of monstrous weight on the shores of 
I^ake Superior, many times weighing from 100 to 200 
tons. The principal ores are, however, (1) chalcopyrite, 
copper pyrites, a sulphide of copper and iron, CuFeS 2 , 
which when pure contains 34.6 per cent, copper; (2) Cup- 
rite, the red oxide, Cu 2 0; (3) Melaconite, the black oxide, 
CuO; (4) Malachite, green carbonate, CuC0 3 , Cu2HO, 
and (5) Chalcocite, copper-glance, the sulphide, Cu 2 S. 

REDUCTION.— This metal is obtained from its ores 
by three different methods, the dry, humid, and electro- 
metallurgical. The process, of course, varies according 
to the nature of the ores treated and local circumstances. 

The dry method is ordinary smelting, and is used for 
ores containing not less than 4 per cent, of the metal, the 



154 PRACTICAL DENTAL METALLURGY. 

wet method being preferred for the poorer ores. In the 
former method the ore is roasted in a reverbatory fur- 
nace, by which much of the iron sulphide is converted 
into oxide, while the copper sulphide remains unaltered, 
and any arsenic that may be present is volatilized. The 
remaining sulphide of copper is now strongly heated 
with silicious sand. The latter combines with the iron 
oxide to form a fusible slag, and separates from the 
heavier copper compound. When the iron has by a 
repetition of these processes been gotten rid of, the cop- 
per sulphide begins to decompose in the flame-furnace, 
losing its sulphur and absorbing oxygen, becoming an 
oxide, which is further reduced by greater heat and car- 
bonaceous matter. The carbonates and oxides are reduced 
in much the same manner, the former being heated to 
drive off the C0 2 , thereby reducing it to an oxide, which, 
with the latter, is further reduced by the aid of a raised 
temperature and added carbon. 

The wet method, which, as previously hinted, is de- 
sirable for ores too poor to yield a profitable quantity by 
the dry method. This method is frequently employed in 
working over what is technically known as (< blue billy" 
or burnt pyrites, which remains as a residue in the man- 
ufacture of sulphuric acid from iron pyrites. Mixed 
with rock-salt and calcined, the small amount of copper 
contained in the iron oxide residue is converted into sol- 
uble cupric chloride, CuCl 2 , and on lixiviating the cal- 
cined mass with water a solution is obtained from which 
the copper may be thrown down in the metallic state by 
scrap-iron. 

Commercial Copper is quite pure, yet it frequently 
contains a small percentage of lead, silver, tin, arsenic, 
and sometimes bismuth and antimony. Arsenic and 
antimony very materially injure the working properties 



COPPER. 155 

of copper, while tin, producing a bronze, increases its 
tenacity and hardness. 

Pure Copper. — The metal may be obtained pure by 
precipitation from the solution of the chloride or sul- 
phate in the presence of metallic iron. Such precipitate, 
a crystalline powder of metallic copper, is called cement 
copper, and is obtained in considerable quantity from the 
sulphate solution found in waters flowing from some 
copper mines. 

PROPERTIES. — Copper, or cuprum, in name is 
derived from Kupros, the Greek spelling of Cyprus, an 
island where it was extensively mined. Its symbol is 
the planet Venus, as the isle of Cyprus was sacred to 
that goddess. It is a peculiar red-colored, brilliant 
metal, differing in this respect from all other metallic 
elements, except, perhaps, titanium. Its atomic weight 
is 63.17, and its specific gravity, 8.94. It takes a brilliant 
polish, and is very malleable and ductile, being second to 
iron in point of tenacity. It may be rolled into thin 
sheets or drawn into very fine wire. A copper wire, 
hard drawn, having a sectional area of a square milli- 
meter, sustained a weight of 90.20 pounds at the moment 
of rupture. The same wire, annealed, broke under a 
weight of 69.52 pounds.* The melting point of copper 
is probably best stated at 1200° C. or 2192° F., and it 
expands slightly on passing from the molten to the solid 
state. It is unaffected by dry air, but in a moist atmos- 
phere it becomes coated with a green carbonate, malachite, 
which is also found native in most beautiful shades, takes 
a high polish, and is used for ornamental articles. When 
heated or rubbed with much friction, it emits a peculiar, 
disagreeable odor. In the conductivity of heat (73.6) 
and elasticity (99.95) it is second only to silver (100). 

* Ganot, Elements de Physique. 



156 PRACTICAL DENTAL METALLURGY. 

DENTAL APPLICATIONS.— Metallic copper has 
long been used for various purposes in the mouth, and 
especially in the form of an attenuated, cone-shaped 
point known as canal-points, for filling pulp canals, 
accompanied with a coating of some plastic-filling sub- 
stance such as chloro-percha. The point is smoothly 
and perfectly tapered in an elongated cone-shape, and 
furnishes a dense, tenacious property, sufficiently rigid 
not to curl upon itself, and yet pliable enough to follow 
the tortuous canal. These are sometimes plated with 
gold for various reasons. 

Very thin sheet copper is cut into narrow strips about 
an inch and one-half long, and used for obtaining the 
circumferential measurement of teeth or roots before 
crowning. 

Dr. Charles B. Atkinson recommends swaging copper 
plate as retaining caps secured by copper wire in the 
treatment of pyorrhea alveolaris,* It is further used as 
concave disks for the protection of exposed pulps, and 
the wire as a ligature for retaining the rubber-dam in 
position. 

The foil in the form of pellets or ropes has been used 
as a filling-material, inserted beneath gold surfaces. 
Also to finish off amalgam fillings, absorbing the surplus 
mercury. 

Copper pans are used for subjecting gold bases during 
the course of construction to the action of boiling dilute 
sulphuric acid. 

Copper poisoning shows a red, or purple-red, or 
"sometimes greenish-brown" (Hirt), line near the mar- 
gin of the gums, says Professor W. D. Miller, and further, 
teeth of copper workers * * * show a more or less 
pronounced greenish discoloration. * * * Teeth 

* Dental Cosmos, Vol. XXXII, p. 549, 



COPPER. 157 

filled with copper amalgam often show a greenish surface 
discoloration.* 

COMPOUNDS WITH OXYGEN.— Copper forms 
two oxides of importance, each of which is found native: 

Copper monoxide, Cupric oxide or Black oxide, CuO, 
is prepared by calcining metallic copper at a red heat in 
the presence of air, or by heating the nitrate to a red- 
ness, driving off the N0 2 * It forms a series of very 
important blue and green cupric salts, isomorphous with 
the salts of magnesium. It imparts a green color to 
glass, and is much used in the chemical laboratory as a 
means of supplying oxygen for the combustion of organic 
substances. When a caustic alkali is added to a cupric 
salt a light blue precipitate, hydrated copper oxide, 
Cu2HO, is formed, which, if heated to 100° C, loses its 
water of crystallization and falls as a black oxide. This 
oxide is soluble in acids. 

Cuprous oxide, Red Oxide, Cu 2 0, occurs in nature as 
a ruby-red octahedral crystal. It may be prepared by 
heating in a covered crucible 5 parts of the black oxide 
and 4 parts of fine copper filings. It gives to glass a 
beautiful ruby-red color. 

The most important cuprous salt is the chloride, CuCl, 
a white solid obtained by dissolving a mixture of cupric 
oxide and metallic copper in hydrochloric acid. It pos- 
sesses a remarkable property of absorbing carbon dioxide. 

ACTION OF ACIDS ON COPPER.— Copper does 
not dissolve in acids with evolution of hydrogen. 

In nitric acid it dissolves most readily, chiefly with 
the evolution of nitric oxides — 

3Cu+ 8HN0 3 =3Cu(N0 3 ) 2 + 4H 2 + 2NO, 
and forming copper nitrate. 

* Dental Cosmos, Vol. XXXVI, p. 265. 



158 PRACTICAL DENTAL METALLURGY. 

In sulphuric acid, hot and concentrated, it also dis- 
solves readily, with evolution of sulphurous anhydride — 

Cu+2H 2 S0 4 =CuS0 4 +2H 2 0+S0 2 , 

and forming copper sulphate — blue vitriol. 

In hydrochloric acid copper is slowly soluble. 

EXPERIMENT No. 44.— In test-tubes containing each of the above acids 
drop small strips of copper plate; heat and note reaction. 

ALLOYS. — The preparation of copper alloys is gen- 
erally attended with many difficulties, on account of the 
high fusing point of the metal and the almost invariable 
presence of small quantities of other elements. 

Mercury with copper readily forms an amalgam of 
definite chemical proportions, having the formula CuHg. 
It crystallizes easily, and on solidifying becomes very 
hard and takes a fine polish. It is also malleable, and 
can be worked under the hammer and between the rollers. 
It retains its metallic luster for some time exposed to air, 
but blackens quickly when in contact with air contain- 
ing sulphuretted hydrogen. It may be softened by heat, 
and is again plastic and flexible, solidifying subse- 
quently. 

These peculiar properties, together with others, led to 
its introduction as a binary dental amalgam, first known 
as Sullivan'' s Amalgam or Cement.* 

Gold and copper alloy readily, the latter giving a de- 
sirable hardness to gold and deepening its color. If, how- 
ever, any considerable proportion of copper be added to 
gold, the alloy is apt to be brittle, especially if the cop- 
per be not absolutely pure. For United States gold coins 
10 per cent, of copper is added to pure gold, giving it a 
carat fineness of 21.6, and a proper degree of hardness 
for durability. 

* See chapter on Amalgams, p.^Sr a^p 



COPPER. 159 

Silver and copper also alloy readily, and the copper 
again gives hardness with a slight change of color. 
Ten per cent, of copper is added to silver for United 
States coin. 

Platinum and copper alloy at an intense white heat, 
giving an alloy much resembling gold in color and 
specific gravity. 

Lead added to copper from l-1000th to 3-1000ths 
somewhat increases its ductility and malleability, but 
the presence of l-1000th renders the metal unfit for 
preparation of malleable or ductile brass. 

Iron to the amount of 3-1000ths also has an injurious 
effect upon the properties of copper, rendering it hard 
and brittle. 

Antimony, bismuth and arsenic in small quantities 
have a very injurious effect upon copper. 

Zinc alloys with copper in any proportion, all of which 
alloys are included in the term brass. Alloys of copper 
and zinc were known in the time of Aristotle, and the 
manufacture of brass was first introduced in Germany in 
1550, but was probably not produced by the direct union 
of the two metals until 1781 in England, as the art of 
obtaining zinc in the metallic form became known but a 
short time previous to that period. Notwithstanding 
copper and zinc may be alloyed in any proportion, the 
product is always serviceable. " Generally speaking, it 
may be said that with an increase in the percentage of 
copper the color inclines more toward a golden, the 
malleability and softness of the alloy increasing at the 
same time. With an increase in the percentage of zinc, 
the color becomes lighter and lighter, and finally shades 
into a grayish-white, while the alloy becomes more 
fusible and brittle and at the same time harder."* 

* Brannt, Metallic Alloys. 



160 PRACTICAL DKNTAI, METALLURGY. 

Alloys containing from 15 to 20 percent, zinc are the most 

ductile. Those of 36 to 40 of zinc can be worked cold 

as well as hot, while those containing 60 to 70 of zinc 

are so brittle that they cannot be worked at all. Raising 

this percentage to from 70 to 90 of zinc, the alloy 

again becomes ductile, and can be worked quite well 

when hot, but not when cold. An alloy of copper 75 

and zinc 25 fuses at 1750° F. 

Good sheet brass may be made according to many 

formulae; two are cited : 

Rosthorn (Vienna) — Copper 68.1 and zinc 31.9 parts. 
Romilly— Copper 70.1, zinc 29.26, lead, 0.38, and tin 0.17 parts. 

For wire, the following : 

England— Copper 70.29, zinc 29.26, lead 0.28, and tin 0.17 parts. 
Neustadt — Copper 71.5 and zinc 28.5 parts.* 

Alloys containing as high as 37 per cent, of zinc are 
used as ductile and malleable products. 

Fine cast brass usually contains from 20 to 50 parts 
of zinc to 100 parts copper, lead, or tin, or both in the 
proportion of 0.25 to 3 per cent, of each.f 

Oreide (French gold) is a brass alloy much resem- 
bling gold. It takes a fine polish and is very ductile, 
malleable, and much used for the manufacture of cheap 
jewelry, on account of its beautiful color. Formula — 
copper 68.21, zinc 13.52, tin 0.48, and iron ' 0.24J, by 
analysis. 

" The most malleable of the brasses is Dutch metal, 
composed of copper 11, zinc 2 parts; it can be rolled out 
into thin sheets and afterward beaten into leaves of 
extreme tenuity, and is used in this form for decorative 
purposes under the name of Dutch leaf-gold or, reduced 

* Figures from Brannt, Metallic Alloys. 
f Ibid. 
J Ibid 



COPPER. 161 

to powder by levigation with a small quantity of oil or 
honey, it is sold as bronze powder."* 

Pinchbeck, an alloy of copper 88.8 and zinc 11.2 
parts, very much resembles gold; is very ductile and 
malleable; used for cheap jewelry. 

Mosaic gold, a term sometimes applied to tin sulphide, 
is composed of about equal parts of copper and zinc. 

Copper coins. — Those of the United States are com- 
posed of copper 95, tin 3, zinc 2 parts. 

Nickel and copper unite in all proportions, the color 
varying from the red of copper to the blue-white of 
nickel, according to the proportions of the respective 
metals: 

Copper with 10 per cent, of nickel gives a light copper- 
colored alloy, very ductile; with 15, the color is a very 
pale red, but the alloy is still quite ductile ; with 25, a 
nearly white alloy, and 30, a silver-white alloy. United 
States nickel coins are composed of copper 75, and nickel 
25 parts. 

Nickel, copper, and zinc alloys are called German 
silver, argentan, etc. They are in reality brasses with 
nickel added, which gives them a white color and much 
hardness. 

These compositions vary greatly as may be noticed: 

Copper 50 to 66 parts. 

Zinc 19 " 30 " 

Nickel 13 " 18 "j 

White Metal . — A variety of alloys consisting of copper 
and a large proportion of zinc. They are very white, or, 
depending upon the proportion of copper, may be a pale 
yellow; melt at a low point, may be cast, and are some- 
what malleable and ductile. 

* Kirk, American System of Dentistry, 
t Brannt, Metallic Alloys. 



162 



PRACTICAL DENTAL METALLURGY. 



Aluminum alloys easily with copper, producing 
aluminum bronze, the alloys showing different properties, 
according to the quantity of aluminum they may contain. 
With 60 to 70 per cent, aluminum, a very brittle alloy is 
produced; with 50 per cent., one quite soft, but less than 
30 per cent, of aluminum, the hardness returns. The 
bronze composed of copper 95, aluminum 5, is a beautiful 
gold color, takes a fine polish, casts well, is malleable 
hot or cold, and is very strong, especially after hammer- 
ing. With 7.5 per cent, aluminum, the color is a 
greenish golden. The most common alloy is 10 per 
cent, aluminum, with yields a bright golden, is not 
tarnished in air, may be engraved, possesses, it is said, 
greater elasticity than steel, and may be soldered with 
20-carat gold solder. It melts at about 1700° F. 

Tin and copper form a very important series of alloys 
termed bronze. (See chapter on Tin.) 

Brazier's Solder. — And alloy composed of copper, 
zinc, tin and lead in a variety of proportions, according 
to color and fusibility, 

Dr. Kirk gives the following table : 





Copper. 


Zinc. 


Tin. 


Lead. 


A 


Golden yellow 

White 


53.50 
43.75 

57.50 


43.33 
50.58 
27.90 


2.12 

3.75 
14.90 




B. 
C. 


1 
trace 









It is used in soldering brass and copper, which may 
also be soldered with the ordinary soft solder, spelter 
(zinc), or silver solder. 

Solders. — Copper is a constituent of most hard solders; 
its proportion varying according to the purpose for 
which they are to be used. (See chapters on Silver and 
Gold.) 



COPPER. 163 

DENTAL-AMALGAM ALLOYS.— Copper is a val- 
uable ingredient in these alloys, and is generally used 
in a proportion varying from 1 to 8 per cent. (See 
Amalgams.) 

TESTS FOR COPPER IN SOLUTION.— Sulphur- 
etted hydrogen added to either acid, alkaline, or neutral 
solutions of copper, throws down a brownish-black pre- 
cipitate of cupric sulphide, insoluble in dilute acids or 
alkilis, but soluble in potassic cyanide. 

Potassium or sodium hydrate throws down a light 
blue cupric hydrate, Cu2HO, insoluble in excess of 
either reagent, but, if heated, falls as the black cupric 
oxyhydrate, (Cu0 2 ) Cu2HO. 

Ammonia, or its carbonate, gives a blue precipitate, 
soluble in excess, producing a deep blue solution. 

Potassium ferrocyanide yields a characteristic brown 
precipitate, soluble in ammonia and decomposed by 
potassa. 

Metallic iron placed in a solution containing copper 
precipitates the latter upon itself in the metallic state. 
Zinc or tin precipitates it as a black powder. 

BLOW-PIPE ANALYSIS.— Copper readily dis- 
solves, from its compounds, in beads of borax and of 
microcosmic salt, in the outer name of the blow-pipe. 
The beads are green while hot, and blue when cold. In 
the inner flame, the borax bead becomes colorless when 
hot; the microcosmic salt turns dark green when hot, both 
having a reddish-brown tint when cold, owing to Cu 2 0. 

Compounds of copper, heated in the inner flame, color 
the outer flame green. Addition of hydrochloric acid in- 
creases the delicacy of the test, giving a greenish-blue 
color to the flame. 

ELECTRO-DEPOSITION OF COPPER.— Copper 
may be deposited by simple immersion from a sulphate 



164 PRACTICAL DENTAL METALLURGY. 

solution. The same solution is used for coating all 
metals and alloys, such as brass and German silver; but 
zinc, iron, lead, steel, tin, Britannia metal, type metal, 
etc., which precipitate it from its solutions by simple 
immersion, are coated in the cyanide or other alkaline 
solutions. Fruits, flowers, insects, etc., may be coated 
with a film of copper from the sulphate solution and a 
single cell. 

Plaster casts of the mouth are easily coated by first 
boiling in wax, and coating when cold with plumbago 
and tin bronze. 



CHAPTER 

IRON. 

Ferrum. 
Valence, II, IV, (Fe 2 ), IV, VI. 
Atomic weight, 55.91. 
Melting point, 1600° (2912° F.). 
Ductility, 4th rank. 
Conductivity (heat), 11.9. 



XIII. 



Symbol, Fe. 
Specific gravity, 7.844. 
Malleability, 9th rank. 
Tenacity, 1st rank. 



Specific heat, 0.1138. 



Conductivity (electricity), 16.81. 
(Silver being 100.) 

Chief ores, Haematite, Magne- 
tite, and Siderite. 
Color, grayish-white. Crystals, cubical. 

OCCURRENCE.— Iron is widely and abundantly 
distributed throughout nature, being found in nearly all 
forms of rock, clay, sand, and earth; its presence in 
these being commonly indicated by their colors, for iron is 
the commonest of all natural mineral coloring ingredients. 

Meteoric Iron. — Metallic iron is very rarely found in 
nature, nearly all of which is probably of meteoric 
origin, with the exception of ferruginous metallic plati- 
num. True meteoric iron usually, if not invariably, 
contains nickel to the extent of 1 or 2 per cent. 

Ores of Iron. — The chief combinations in which iron 
is found in sufficient quantity to render them available 
sources of the metal are shown in the table below:* 



Common Nanie. 



Magnetic iron ore 
Red haematite. . . 
Specular iron . . . 
Brown haematite. 
Spathic iron ore. 
Clay iron-stone . . 

Blackband 



Iron pyrites, 



Chemical Name. 



Composition. 



Fe 3 4 , 



Protosesquioxide of Iron . . 

Sesquioxide Of Iron Fe, 

Sesquioxide of Iron Fe, 

Hydrated sesquioxide of Iron 2Fe 2 3 .3H 2 0. 

Carbonate of Iron FeO.CO,. 

Carbonate of Iron, with clay . | 

I Carbonate of Iron, with clay ] 

\ and bituminous matter 

Bisulphide of Iron FeS ,. 



* Bloxam's Chemistry Inorganic and Organic, p. 332. 



166 PRACTICAL DENTAI, METALLURGY. 

Magnetic Iron. — Magnetite, or loadstone, Fe 3 4 , is 
found massive in very large quantities in Norway, 
United States, Canada, New Zealand, and India. The 
ore of Norway furnishes the Swedish iron of such excel- 
lent quality, and the sands of New Zealand and India the 
excellent Wootz steel. It contains, when pure, about 72 
per cent, of iron. 

Red hcematite, Fe 2 3 , is found in abundance in Eng- 
land, occurring in hard, shining, rounded masses of a 
dark red-brown color. It is a very characteristic ore of 
iron, containing from 47 to 70 per cent, of the metal. 

Specular iron, like red haematite, is an anhydrous 
sesquioxide (Fe 2 3 ), but differs greatly in appearance, 
being of a steel-gray color and brilliant luster. It occurs 
chiefly on the island of Elba, but is also found in Ger- 
many, France, and Russia. The excellent quality of iron 
obtained from this is probably due to the purity of the 
ore, and to the fact that charcoal, instead of coal, is em- 
ployed in smelting it. It contains about 62 per cent, of 
iron. Red ochre is a. soft variety of this ore, containing clay. 

Brown hcematite, limonite, 2Fe 2 3 .3H 2 0, is the hy- 
drated sesquioxide. It is of a distinctly sedimentary 
character, forming beds, but is also found in veins. It 
occurs principally in Belgium and France, and contains 
about 15 per cent, water, and, when pure, about 59 per 
cent. iron. Yellow ochre is a variety of this ore. 

Spathic ore, siderite, ferrous carbonate, FeO.C0 2 , or 
FeC0 3 . The value of this ore depends as much upon 
the nature of its impurities as upon the percentage of 
iron. It is found in Saxony of a crystalline character, 
light brown or gray in color, having a pearly luster, and 
when pure contains about 48 per cent. iron. 

Iron pyrites, FeS 2 , is particularly remarkable for its 
yellow color, brilliant metallic luster, and crystalline 



IRON. 167 

structure, from which facts it has been termed ' ' fool's 
gold." It does not form a direct source of iron, but the 
residue left after burning pyrites to make sulphuric acid, 
and extracting the copper,* is almost entirely of ferric 
oxide, from which iron is ultimately reduced. 

REDUCTION. — If the ore is a carbonate, or contains 
any carbonate, it is usually first calcined, by roasting in 
a kiln or in long pyramidal heaps, resting upon founda- 
tions of large lumps of coal, to expel the water and 
carbon dioxide. This process reduces the ore to a dry, 
porous mass, and the iron to an oxide. Much of the 
sulphur, nearly always present, is driven off as sulphur 
dioxide at the same time. 

The calcined ore is then mixed with a certain propor- 
tion of limestone (calcium carbonate) as a flux, which is 
to induce the earthy part of the ore to flow, in order to 
liberate the iron. With the proper quantity of coal, 
coke or charcoal, it is then introduced into one of the 
great blast-furnaces. f 

It would be very easy to reduce the oxide contained 
in the calcined ore to metallic iron in such a furnace 
when heated with carbon; but the metallic iron fuses 
with so great difficulty that it is impossible to separate 
it from the clay, unless the latter is brought to a liquid 
state, and even then the fusion of the iron, which is 
necessary for complete separation, is only effected after 
it has formed a more easily fusible compound with the 
small proportion of carbon derived from the fuel. The 
clay is even more difficult to fuse than the iron, so it is 
necessary to add with the ore to be smelted some sub- 
stance capable of forming with clay a combination which 
is fusible at the temperature of the furnace. As has been 

* See chapter on Copper. 

t See chapter on Melting Metals, p. 61, Fig. 2. 



168 PRACTICAL DENTAI, METALLURGY. 

previously stated, limestone produces the required result 
by forming the double silicate of alumina and lime, 
which becomes perfectly fluid. 

As the air passes from the tuyere (at B\ Fig. 2) pipes 
into the bottom of the furnace, it parts with its oxygen to 
the carbon of the fuel which converts it into carbon 
dioxide (COJ; this latter passing over the red-hot fuel 
as it ascends in the furnace is converted into carbon 
monoxide (CO) by combining with an additional quan- 
tity of carbon. It is this carbon monoxide which reduces 
the calcined ore to the metallic state, when it comes in 
contact with it, at a red heat, in the upper part of the 
furnace, for this abstracts the oxygen, at a high temper- 
ature, from the oxides of iron; itself becoming carbon 
dioxide, the iron remaining in a free state. The metal 
as it melts, being the heavier, sinks by its own gravity 
through the fuel into a crucible or cavity (A, Fig. 2) at 
the bottom of the furnace; as it sinks, however, it com- 
bines with a small proportion of carbon to form cast iron. 
At the same time the fluid slag, composed of the clay, 
or earth, made fluid by the addition of carbonate of 
lime as a flux, sinks also into the crucible, built at the 
bottom of the furnace, where it forms a layer of slag 
over the molten metal. When the slag so accumulates 
that no more will be contained in the crucible, it is 
allowed to run over its edge down the incline (E in Fig. 
2) on which the furnace is built. Thus the process is 
carried on until there is sufficient metal melted to consti- 
tute what is termed a charge, which rises almost to the 
aperture of the blast. The furnace is then tapped, at an 
opening provided for that purpose, and the metal run off 
into molds, when it is cast into rough, semi-cylindrical 
masses called pigs — crude cast iron. For purposes where 
hardness without flexibility is wanted, the remelted iron 
of this state is extensively used. 



IRON. 169 

PROPERTIES.— Pure iron is a hard, malleable, duc- 
tile, and tenacious metal, of a grayish-white color, and 
of fibrous texture, a slightly styptic taste, and a sensible 
odor when rubbed. Its strength and tenacity are very 
high. In magnetic characters it is superior to all other 
substances, nickel and cobalt being next; when it is 
almost pure, the magnetic influence produced, owing to 
induction, by the proximity of a permanent magnet or 
of an electric current, disappears entirely on removal of 
the magnet or current; if, on the other hand, carbon be 
present, (as is usually the case to some small extent even 
in the softest malleable iron), there remains after the 
removal of the magnet or current a greater or less 
amount of permanent magnetism, according to the cir- 
cumstances, hard steel exhibiting the greatest power of 
becoming permanently magnetized under given con- 
ditions. In thermic and electric conductivity iron is 
11.9 and 16.81 respectively. Its specific gravity is 7.844, 
its specific heat 0.1138, and its melting point is variously 
estimated from 1500°-1600° C (Pouillet) to 1900°- 
2000° C. (Deville). The presence of minute quantities of 
carbon, sulphur, etc., very sensibly lowers the fusing 
point, whilst 1 per cent, of the former furnishes a steel 
melting at several hundred degrees lower than pure iron. 
Cast iron, containing more carbon, melts very much 
lower. It possesses the remarkable property of becom- 
ing plastic just before fusion, so that two hot masses 
may be pressed or squeezed together into one by the 
process of welding. So by forging, rolling, hammering, 
or other analogous operations, it can readily be fashioned 
into shapes which its rigidity and strength when cold 
will enable it to maintain. It is combustible, and, when 
heated to whiteness, burns in atmospheric air, and with 
brilliant scintillations in oxygen gas. It combines with 



170 PRACTICAL DENTAL METALLURGY. 

all the non-metallic elements, except hydrogen and nitro- 
gen, and with most of the metals. 

MODIFICATIONS OF IRON.— There are three dis- 
tinct modifications of iron, viz., cast iron, wrought 
iron, and steel. Other immediate varieties are recog- 
nized technically, but all are closely related and 
imperceptibly shaded into each other, due to various 
percentages of carbon, etc., contained in the metal. 

CAST IRON is an impure carburized iron. The 
melted metal drawn off from the furnace below is con- 
ducted into a large main, called the "sow" and thence into 
lateral molds called ' 'pigs " ; hence the term pig iron. This 
iron is found to have combined with a considerable quan- 
tity of carbon, about 4.5 per cent, being the maximum; a 
portion of which exists as a chemical combination, the 
carbide of iron, the remainder having been simply dis- 
solved in the form of graphite. Other substances in the 
furnace are also found dissolved and combined in the 
iron, and have an important bearing upon its physical 
properties. These are principally phosphorus, silicon, 
sulphur, manganese, etc. 

Pig iro?i may, therefore, be recognized as a crude form 
of cast iron. It is assorted and classed by the iron 
masters as Nos. 1, 2, and 3, differing in the amount of 
carbon contained. No. 1 is most highly carburized, No. 
2 less, and No. 3 contains the least carbon. The first 
melts and runs so fluid that it is used for ornamental 
castings of fine pattern, and furnishes cast-iron cutlery 
from which the carbon is subsequently extracted. 

Cast iron, which contains the most carbon, is the most 
fusible variety, melting at about 1200° C. It is hard 
and brittle. Though some kinds admit of being made 
hard or soft nearly in the same manner as steel, and, like 
steel, assumes different degrees of hardness, according to 



IRON. 171 

the rapidity with which the pieces are allowed to cool; 
but unlike steel, when once hardened, will not admit of 
that hardness being reduced by various gradations to 
any specific degree, called tempering. To soften mate- 
rially it must be submitted for some time to a whitish 
heat, and then very gradually cooled. 

WROUGHT IRON is the cast, or pig, iron, freed from 
carbon, and may be considered a nearly pure decarbur- 
ized iron ; at least, it is the purest form of commercial iron , 
containing the least amount of carbon — less than % per 
cent. The decarburization is effected by first remelting 
the pig, or cast iron, and refining by exposing it to an 
intense heat and forcing a blast of air over its surface, in 
order to remove some of the impurities of the metal; it 
is then run out into a large flat mold, and acquires the 
name of plate metal. 

The next process is called " puddliiig" the object 
being to free the metal of its carbon. The operation is 
conducted in a reverberatory furnace, where the metal 
is again reheated and converted into wrought iron by 
keeping it in a state of fusion with a certain amount of 
black oxide of iron, Fe 3 4 , which gives up its oxygen 
after a time to the carbon, and other impurities of the 
melted mass, leaving the latter nearly pure iron. As the 
process approaches termination the fusing point of the 
mass grows higher, until it loses nearly all its fluidity. 
It is then divided into several parts and formed into 
balls, which are removed from the furnace and subjected 
to intense pressure through a series of powerful rollers, 
which squeeze out the more fusible slag entangled in 
it and convert it into bars or "blooms" A number of 
these blooms are then raised to a welding heat and re- 
peatedly passed through rollers, until all the remain- 
ing slag is forced out and the metal becomes tough and 



172 PRACTICAL DENTAL METALLURGY. 

fibrous. Thus the process is repeated, usually once, and 
sometimes — to produce a superior iron — twice or three 
times. By this process the metal is converted from a 
fusible, hard and brittle substance, as cast iron, into a 
tough, elastic bar; in fact, it has been rendered malle- 
able, ductile, more closely compact, and of a fibrous tex- 
ture, and is hardly fusible. It is also very tenacious, 
and added to its properties is a new and remarkable one, 
by virtue of which two pieces being heated similarly 
may be forged or welded together. For purposes where 
lightness, strength, and durability are wanted, it is more 
extensively employed than cast iron. In this state it is 
known in commerce as bar, or wrought, iron. 

STEEL is composed of iron and carbon, and is some- 
times formed from wrought iron, by heating the latter in 
contact with carbon, and sometimes from cast iron, by 
depriving it of impurities, and all but a small percentage 
of carbon. The proportion of carbon varies, of course, 
in the different qualities of steel; but in that used 
ordinarily the carbon rarely exceeds one and one-half per 
cent.; for some purposes it is as low as one per cent. 
Good ordinary tool steel contains about one and one-half 
per cent, of carbon. 

Different kinds of iron produce steel of different prop- 
erties, and different qualities of steel are used for different 
purposes. 

There are two distinct processes employed for the pro- 
duction of steel, known as the Cementation Process and 
Bessemer's Process. By the latter process steel can 
be manufactured of any degree of hardness directly from 
the cast iron, without the intermediate operation of 
making it malleable by puddling, etc. The principle of 
the process consists in directing a blast of cold air upon 
molten cast iron contained in a "converter." The oxygen 



IRON. 173 

of the blast combines with the carbon, silicon, and man- 
ganese. Sulphur and phosphorus are difficult to remove 
by this process; hence the necessity of employing ores as 
free from these as possible. The intense combustion of 
the carbon in the iron is attended with great elevation of 
temperature, so that the metal is maintained in a fluid 
state throughout the whole operation, solely by the 
energy of the reaction in the converter. Thus the cast, 
or pig, iron is decarburized, or converted into tool steel, 
or to mild welding steel, or to the state of malleable 
iron, according to the length of time the combustion is 
continued. It has been found, however, that a better 
quality of steel can be produced by continuing the 
decarburizing and purifying process until all, or as nearly 
all as possible, of the carbon and impurities are removed, 
and then adding to the fused wrought iron a certain 
quantity of a peculiar kind of white cast iron known as 
spiegel-eiseri* (" looking-glass " iron), containing a known 
quantity of carbon and a little manganesium. 

Bessemer steel is largely used in the construction of 
railroads, bridges, armor plates for vessels, girders, etc., 
in the construction of edifices, the manufacture of ma- 
chinery, tools, etc., and there is good reason to believe 
that steel of an excellent quality for numerous purposes 
will, at no distant period, be manufactured cheaper than 
wrought iron is now produced by the operation of pud- 
dling. 

The Cementation Process. — The furnace in which 
the iron is cemented and converted into steel, called a 
converting furnace, has the form of a large oven, con- 

* Spiegel-eisen is composed of the following: 

Iron 82-86 

Manganesium 10.71 

Silicon 1.00 

Carbon 4.32 



174 PRACTICAL DENTAL METALLURGY. 

structed so as to form in its interior two large and long 
cases, commonly called troughs or pots, and built of good 
fire-stone or fire-brick. Into each of these pots layers of 
the purest malleable iron bars, and layers of pulverized 
charcoal are packed horizontally, one upon the other, to 
a proper height and quantity, according to the size of 
the pots, leaving room every way in them for the expan- 
sion of the metal when it becomes heated. After the 
packing is completed the tops are covered with a bed of 
sand or clay. This is to confine the carbon and exclude 
the atmosphere. The whole is then heated for eight or 
ten days, according to the degree of hardness required. 
Then the mass is left to cool for several days. 

The properties of the iron are remarkably changed by 
this process: it acquires a small addition to its weight, 
becomes much more brittle and fusible than originally, 
loses much of its ductility and malleability, but gains in 
hardness, elasticity, and sonorousness. The texture, 
which was fibrous before, has now become granular; 
and its surface is found to be covered with blisters, and 
it presents, when broken, a fracture much like inferior 
iron. Iron under this process has been shown to have 
taken up about 1 per cent, of carbon. It is, however, 
far from being homogeneous in composition, and is called 
blister steel. Uniformity of composition is secured by 
subjecting bundles of the carburized bars to repeated 
blows from a steam-hammer at a welding heat, striking 
in rapid succession, until it closes the seams and removes 
the blisters. It is then termed shear steel. After this 
treatment is repeated it is called double-shear steel. 
Homogeneity is best obtained, however, by fusing the 
blister steel in crucibles, covering the mass with clay or 
some other substance to exclude air, and casting it into 
ingots. It is then designated as cast steel. 



IRON. 175 

Spring steel is blister steel simply heated and rolled. 

Case hardening is accomplished by heating such articles 
of forged, or bar, iron, as it is desired to harden super- 
ficially in contact with some substance rich in carbon, 
and afterwards chilling them in water. Gun-locks are 
thus treated. 

Red-short. — Sulphur when present in as small a pro- 
portion as 0.1 per cent, serves to make the metal brittle 
and liable to fracture when worked or rolled at red heat, 
hence the term. 

Cold-short. — Phosphorus, when present, renders the 
steel brittle when cold. It serves, however, to neutralize 
the effect of sulphur; but steel containing phosphorus 
is extremely difficult to temper. 

Nickel Steel.— In 1889, M. Henry Schneider of 
Creusot, France, patented an alloy of steel and nickel. 
The alloy usually contains about 5 per cent, of nickel, 
and is especially suitable for use in the construction of 
ordnance, armor-plate, gun-barrels, and projectiles. It 
is said that ordinary steel is more readily acted upon by 
sea water than are the more impure grades of iron, but 
nickel steel is less liable to corrode in salt water than 
ordinary steel. 

Chrome Steel. — Chromium gives greater hardness, 
tensile strength, and elasticity to iron, but decreases its 
weldability. It is also stated that chromium steel is 
more susceptible to oxidation than ordinary steel. 
Chromium is added to iron by heating the mixed oxides 
of iron and chromium in a brasqued crucible with pul- 
verized charcoal and fluxes. Chrome steel is then 
produced by melting chrome iron with wrought iron or 
steel in graphite crucibles. 



176 PRACTICAL DENTAL METALLURGY. 

Manganese Steel. — When about 15 per cent, of man- 
ganese is added to steel it produces an alloy of great 
strength and toughness, and so hard that it is almost 
impossible to work the product by ordinary methods. 
The alloy is usually prepared by adding manganese iron 
to molten Bessemer, or open-hearth steel. From 4 to 5 per 
cent, of manganese gives to the alloy its extreme brittle- 
ness. Extremes of atmosphere, heat or cold, do not 
appear to effect the properties of manganese steel. When 
a piece of it heated sufficiently to be seen red hot in a 
dark room is plunged into cold water, it becomes soft 
enough to be easily filed. Hardness is then restored by 
reheating to a bright red and cooling in air. 

Copper Steel. — This alloy usually contains from 5 to 
20 per cent, of copper, according to the purpose for 
which it is to be used. It possesses remarkable strength, 
tenacity, and malleability, and these properties are still 
further developed by tempering. 

Aluminum Steel. — In amounts not greater than 1 per 
cent, aluminum is said to slightly increase the tensile 
strength, and proportionally the elastic limit, of rolled 
and cast steel. 

Tungsten in small quantities produces an exceedingly 
hard steel, without the necessity of tempering. 

CARBURIZED IRON.— As has been previously 
hinted, carbon may be present in iron under two con- 
ditions. When iron is "fused in contact with carbon 
[it] is capable of combining with nearly 6 per cent, of 
that element, to form a white, brilliant, and brittle com- 
pound, which may be represented pretty nearly as Fe 4 C. 
Under certain circumstances, as this compound of iron 
and carbon cools, a portion of the carbon separates from 



IRON. 177 

the iron and remains disseminated throughout the mass 
in the form of minute crystdline particles very much 
resemblng natural graphite."* 

Iron containing the least possible carbon, and other- 
wise comparatively pure, is called wrought iron. 

Iron containing from 1.04 to 4.81 per cent, of carbon is 
•designated as cast iron. 

Iron containing from 0.15 to 1.04 (Bloxam) is con- 
sidered steel. ' ' The portion of combined carbon within 
certain limits bears a direct relation to the tensile strength 
of the metal, variations as minute as one-hundredth of 
1 per cent, making a considerable alteration in this qual- 
ity. The same is true of hardness, the effect of carbon 
up to a certain point being to increase tenacity and de- 
crease ductility, and also to cause the metal, when heated 
and suddenly cooled, to become more or less hard, the 
hardening being in direct proportion to the amount of 
carbon present and the rate of cooling, "f 

1.4 per cent, of carbon in iron produces a highly car- 
burized steel that must be worked with great care. It 
should not be heated above a cherry-red, for fear of 
burning. Such steel is used for the manufacture of 
razors and tools for cutting hard metals. 

Steel containing from 1 to 1.25 per cent, of carbon is 
used for making most tools. 

Steel containing about 1 per cent, of carbon can be 
welded readily, and a portion of a tool made of it can be 
made tough, so as to stand a blow from a hammer, with- 
out chipping, while another part can be hardened, as in 
the case of a cold-chisel. 

*Bloxam's Chemistry, Inorganic and Organic, p. 340. 
f Kirk, American System of Dentistry, Vol. Ill, p. 900. 



178 PRACTICAL DENTAL METALLURGY. 

HARDENING AND TEMPERING STEEL.— -After 
soft steel has been shaped into the form of instrument 
desired, it may be made as hard as diamond, by first 
heating to redness and then immediately chilling by 
plunging into cool water, oil, or mercury. It appears in 
heating steel and quickly chilling it a greater proportion 
of the carbon is chemically combined with the iron, 
forming the carbide; but if the hardened steel be heated 
to redness again and allowed to cool slowly, it returns to 
its soft condition, in which it has been found that a 
greater proportion of the carbon seems to be only inti- 
mately mixed with the iron, as graphite, for it is left 
undissolved in treating the soft steel with acid. Any 
desired variation between these two extremes may be 
obtained by first rendering the metal full hard, by heat- 
ing to redness and quickly chilling it, and then carefully 
reheating it to the proper point at which the desired 
degree of temper is produced, and discontinuing the 
heating that instant, and suddenly chilling in cool water. 

If brightened steel be heated gradually and carefully 
over a flame, it will take on a succession of shades and 
colors, owing to the formation of a film of oxide which 
grows thicker and of deeper shade and color as the heat- 
ing progresses. The temperature at which given degrees 
of temper are produced has been carefully determined, 
and the experienced operator knows by the shade or 
color of the film of oxide the temper of the instrument 
operated upon, provided the piece is known to be steel 
and to have been full hard. 

The following table shows the approximate tempera- 
tures corresponding to the various shades and colors: 



IRON. 



179 



Temperature. 

430° to 450° F. 

470° 

490^ 

510° 

530° 

550° 

560° 

600° 



Color. 

Very faint yellow 
to pale straw. 

Full yellow 

Brown 

Brown with pur- 
ple spots 

Purple 

Bright blue 

Full blue 

Dark blue 



Temper. 

Lancets, razors, surgical in- 
struments, enamel chisels. 

Excavators, very small cold- 
chisels 
j Pluggers, scissors, pen- 



knives. 

Axes, plain irons, saws, cold- 
chisels. 

Table knives, large shears. 

Swords, watch springs. 

Fine saws, augers. 

Hand and pit saws. 



Since the amount of hardness which can be developed 
in steel is directly in proportion to the amount of carbon 
and rate of cooling the article from the heated condition, 
and as pieces of steel vary greatly in their content of 
carbon, the temperature at which it is necessary to heat 
them before chilling must be determined by actual exper- 
iment, in order to produce the greatest hardness. The 
piece should never be overheated. It is better, says 
Dr. Kirk, to err upon the side of under- instead of over- 
heating, for under the latter condition the steel is burned, 
presents a blistered, scaly appearance, and is incapable 
of taking a fine temper. When small instruments, such 
as burs, excavators, etc., are to be hardened, it is best to 
protect the surface of the steel with some substance to 
prevent a loss of carbon by oxidation in the heating. 
" Common soap answers admirably for this purpose," 
says Dr. Kirk. 

The means of applying the heat to articles when they 
require hardening will, of course, depend upon the size, 
shape, and use of the article. They may be heated in 
the flame of the Bunsen burner, alcohol lamp, open fire, 
and sometimes it is best to enclose them in a sheet-iron 
case with carbon, and heat in a suitable furnace; but for 



180 PRACTICAL DENTAL METALLURGY. 

a more uniform degree of heat red-hot lead is probably 
better than any other means. 

In chilling, water is by no means essential, as the sole 
object is to extract the heat as rapidly as possible by 
good conduction; and the more suddenly the heat is ex- 
tracted, the harder the steel will be; but if the hardness 
is not carried to an extreme, a certain amount of tenacity 
is also obtained with the hardness. 

Water with a small amount of acid or salt is some- 
times used, the former to aid in removing the oxide, and 
the latter to increase the conductivity. For extreme 
hardness mercury is used, which, on account of its 
superior conductivity, chills the piece immediately. 

TEMPERING.— A rod of good steel in its hardest 
state is broken almost as easily as a rod of glass of the 
same dimensions. This brittleness can only be dimin- 
ished by decreasing its hardness; and the management 
of this is called tempering . The surface of the steel is 
brightened and tried with a fine file to make sure of its 
full-hardness, and is then exposed to the heat, which, 
upon the appearance of the color desired and previously 
determined upon, is discontinued, and the article cooled 
by instantly plunging into cool water. The methods for 
applying the heat for tempering are as varied as those 
for hardening. The heat for this purpose should be 
slowly applied; indeed, it is said that the slower the heat- 
ing, the tougher and stronger will be the steel. The 
article may be placed upon a hot iron plate, upon the 
surface of melted lead, or in a bath of a more fusible 
alloy; in hot sand, a gas stove, or in almost any place 
where sufficient temperature may be gradually obtained, 
without injury to the steel. 

The following table of alloys of lead and tin may be 
conveniently used to secure a uniform temper: 



IRON. 



181 



Composition. 


Melting Points. 
Degrees F. 




Lead. 


Tin. 




7. 


4 

4 
4 
4 
4 
4 
4 
4 
4 


420° 




7.5 


430° 


8.5 


450° 




10. 


470° 


14. 


490° 


19. 


510° 


30. 


530° 


48. 


550° 


50. 


560° 






Boiling 


oil 


600° 







(Compare the degrees with the colors of previous table.) 

When instruments are only partially dipped and 
afterwards tempered by the heat from the back, they 
must be cooled in water, or other substance, instantly on 
the cutting part attaining the desired color; otherwise 
the body of the instrument will continue to supply heat, 
and the cutting part may become too soft. In the case 
of excavators, enamel chisels, and cutting instruments 
with slender, tapering shanks, terminating in a fine cut- 
ting-edge, the edge must be protected from the heat while 
tempering the shank, the latter being drawn to a blue, 
a state much too soft for the former. The point or edge 
may be protected by placing against a large piece of cold 
iron or other substance, which, on account of its conduc- 
tion, prevents the heating of the end of the instrument. 

Rubber-dam clamps are best tempered a blue spring 
by what is known as blazing off. This is accomplished 
by dipping them in oil, and then burning the oil off. 

EXPERIMENT No. 45.— The student should be furnished suitable blanks 
of good steel for making enamel chisels, excavators, pluggers, and clamps, 
and required to make and properly temper them. 

COMPOUNDS WITH OXYGEN.— Iron forms three 
compounds with oxygen: 



182 PRACTICAL DENTAL METALLURGY. 

Monoxide, Ferrous Oxide, FeO, is a very powerful 
base, but is almost unknown in the separate state on 
account of its proneness to absorb oxygen and pass into 
the sesquioxide. 

Sesquioxide, or Ferric Oxide, Fe 2 3 , is a weak base, 
and occurs native in most beautiful crystals as specular 
iron ore; also as red and brown haematite. It may be 
artificially prepared by precipitating a solution of ferric 
sulphate or chloride with excess of ammonia, washing, 
drying, and igniting the yellowish-brown hydrate thus 
produced. It is of a red color, the tint varying with the 
temperature at which it has been exposed. It occurs 
commercially under the name of colcothar ■, jeweler 's rouge, 
and Venetian red, which is obtained by calcining the 
green sulphate of iron — 

2(FeO.S0 3 )=Fe 2 3 + S0 2 + S0 3 . 

It is dissolved in acids with difficulty, forming a series 
of reddish salts. 

Triferro-tetroxide, Ferroso-ferric Oxide, Fe 3 4 , is also 
called black iron oxide, magnetic oxide, and loadstone. It 
occurs native, and is one of the most valuable of the iron 
ores. It is the chief product of the oxidation of iron 
at a high temperature in the air and in aqueous vapor. 

ACTION OF ACIDS ON IRON.— Iron dissolves in 
the acids, and the carbon which it always contains, so 
far as combined in the carbide of iron, passes off as car- 
buretted hydrogen, and so far as uncombined will 
remain undissolved, as graphite. 

In dilute sulphuric acid iron dissolves, forming fer- 
rous sulphate, liberating hydrogen — 

Fe+H 2 S0 4 =FeS0 4 +H 2 . 

In hydrochloric acid it dissolves, to form ferrous 
chloride, with liberation of hydrogen. 



IRON. 183 

In nitric, cold and dilute, it is soluble, forming ferrous 
and ammonium nitrate — 

4Fe+ 10HNO 3 =4Fe(NO 3 ) 2 -f H 4 NN0 3 + 3H 2 0, 

and in warm, dilute nitric to form ferric nitrate, liberat- 
ing nitric oxide — 

2Fe + 8HN0 3 =Fe 2 (N0 3 ) 6 + 2NO+4H a O. 

ALLOYS. — Iron combines with many of the metals. 
None of its alloys are of any great importance. 

With mercury, iron cannot be made to combine 
directly, yet Bloxam claims that it forms a chemical 
combination with this element, having the formula 
FeHg. The combination is effected by adding a little 
amalgam of sodium to the metallic mercury. The amal- 
gam may also be prepared by "rubbing together very 
finely divided iron with mercuric chloride and water and 
a few drops of metallic mercury. Pure amalgam of iron 
forms lustrous white crystals, which, however, soon be- 
come coated with rust. By lying in the air the iron 
contained in the amalgam is in a short time converted 
into ferric oxide, which floats upon the metallic mer- 
cury. "* 

It alloys somewhat with the noble metals; also with 
tungsten, titanium, chromium, and manganesium. 

An alloy of cast iron 79, tin 19.50, and lead 1.50, 
may be used as a casting metal, giving fine impressions, 
filling the molds, and being malleable to a certain 
extent. 

Arnold's Iron Alloy. — Crude cast iron, 100; soda, 1; 
copper, 1; tin, .5; antimony, .5, and zinc, 5. A com- 
pact and malleable alloy, capable of taking a fine polish, 
and resisting the corrosive action of sea water. It is used 
for ship's screws. 

* Brannt, Metallic Alloys, p. 363. 



184 PRACTICAL DENTAL METALLURGY. 

Marlie's Non-oxidizable Alloy. — Iron, 10 parts; 
nickel, 35; brass, 25; tin, 20, and zinc, 10. 

TESTS FOR IRON IN SOLUTION. — Ferrous 
salts. — The solutions are green, and sulphuretted hydro- 
gen produces no precipitate in an acid solution, but may 
give a slight one in a neutral solution. 

Ammonium hydro-sulphide gives a black precipitate 
of ferrous sulphide, insoluble in excess of the precipitant. 

Potassium ferric-cyanide is the characteristic test; it 
throws down a deep blue precipitate (Turnbull's blue). 

Ammonia throws down hydrated ferrous oxide (the 
antidote for arsenic*). This is, at the moment of forma- 
tion, white, but passes rapidly through the shades of 
light green, dark green, and ultimately brown — the latter 
being an indication of its conversion into ferric oxide. 

Ferric Oxide. — Potassium ferro-cyanide is a charac- 
teristic test, producing a precipitate of Prussian blue. 

*It should be the invariable rule of every dentist to keep on hand in his 
office the materials for preparing this antidote, for an emergency, as it should 
be freshly prepared at the ti7ne of ?teed. A very efficient antidote may be pre- 
pared by precipitating the tincture of the chloride of iron with bicarbonate of 
sodium. 



CHAPTER XIV. 

ALUMINUM. 

Aluminum. Symbol, Al. 

Valence, III, (A1 2 ) VI . Specific gravity, 2.583. 

Atomic weight, 27. Malleability, 2d rank. 

Melting point, 700° (1292° F.). Tenacity, 4th rank. 

Ductility, 7th rank. Chief ore, cryolite. 

Conductivity (heat), 100. Conductivity (electricity), 100. 

(Silver being 100. > 

Color, bluish-white. Crystals, octahedral. 

OCCURRENCE.— With the exception of silicon and 
oxygen, aluminum is the most abundant element in the 
earth's crust. It is found, combined with silicon and 
oxygen, as marl, clay, slate, pumice-stone, feldspar, 
mica, and nearly all rocks, with the exception of lime- 
stone and sandstone. As the crystallized oxide — alumina 
— it occurs as corundum, emery, ruby, sapphire, 
emerald, topaz, and amethyst, which are used as gems. 
The metal is further found in combination with nearly 
two hundred different minerals. 

REDUCTION.— It was first isolated in 1828, by 
Wohler, who obtained it as a gray powder by decompos- 
ing aluminum chloride with potassium. It remained a 
laboratory product until St. Claire Deville, about 1858, 
succeeded in improving the mode of production, so as to 
render the operations capable of management on a manu- 
facturing scale. The process consists in heating to a red 
heat the double chloride of aluminum and sodium with 
metallic sodium. A vigorous action takes place, chloride 
of sodium being formed and the metallic aluminum sep- 
arated — 

AlC1 3 .NaCl+3Na=Al+4NaCl. 



186 PRACTICAL DENTAL METALLURGY. 

On a large scale the reduction is effected by throwing 
a mixture of 10 parts of the double chloride, 5 parts of 
the double fluoride (AlF 3 .3NaF, cryolite), and 2 parts 
sodium on the hearth of a reverberatory furnace. Im- 
mediately after the action, the fused metal and slag, con- 
sisting of common salt and fluoride of aluminum, are 
run out, and a new quantity of the previous mixture in- 
troduced. The various patents which have been secured 
in reference to this manufacture have all regard to the 
saving of the metal sodium. 

The metal is extensively reduced through the inven- 
tion of the Cowles' electrical furnace, which consists of a 
rectangular box of fire-brick lined with limed charcoal. 
The crushed ore is mixed with fine charcoal, and the 
iron cover of the furnace adjusted. A powerful current 
from a dynamo-electric machine is then passed into the 
furnace by means of two carbon electrodes. After about 
five hours the furnace is allowed to cool, and the metallic 
aluminum and slag removed. 

PROPERTIES.— Aluminum is a bluish-white metal, 
somewhat resembling silver in appearance. It is also 
said to be as malleable, of the same tenacity, and equal 
to. that metal in the conduction of heat and electricity. 
It is harder than tin, but softer than copper. By ham- 
mering in the cold it may be made as hard as soft iron, 
but is softened again by fusion. It is remarkably sonor- 
ous, and has been used for making bells. It is one of the 
lightest of metals, being approximately only 2}i times 
heavier than water, and 4 times lighter than silver. 
It fuses at 700° C, or about 1300° F.; does not oxidize in 
air, even at a red heat; has no action on water at ordi- 
nary temperatures, nor is it acted upon by the compounds 
of sulphur, thus preserving its luster where silver would 
be tarnished and blackened. It is without odor or taste. 



ALUMINUM. 187 



IN THE ARTS aluminum is used in the manufacture 
of weights of small denomination, such as the milligram; 
its low specific gravity rendering it particularly well 
adapted to that use. It is further used, on account of its 
lightness and resistance to atmospheric action, for the 
manufacture of delicate physical, mathematical, and 
optical apparatus, as well as ornamental articles, such as 
medalions and badges of a souvenir character; also for 
parts of bicycles, tablewear, and cooking utensils. The 
apex of the Washington Monument is of highly polished 
aluminum. 

IN DENTISTRY this metal is employed as a 
base for artificial dentures. Its many valuable proper- 
ties, chiefly conductivity, lightness, malleability, cheap- 
ness, and unalterableness in dry or moist air, render it 
applicable for such a purpose. The base is swaged 
between a zinc die and lead counter-die, but will not stand 
the rough swaging sometimes given to gold or platinum. 
Caution must be used to prevent contamination with the 
lead or zinc. It being difficult to determine during the 
progress of the conformation whether or not any con- 
tamination has occurred; the pattern is best swaged be- 
tween thin tissue paper, removing the paper as it 
becomes broken. The metal should be occasionally 
annealed by coating with pure sweet-oil or tallow, and 
passing through the flame until the oil or fat is carbon- 
ized, when at the moment the last trace of black (carbon) 
disappears from the metal, it may be dropped into water. 
Before applying the oil and annealing, however, the metal 
should be thoroughly brushed with pumice-stone, to 
remove any contaminating lead or zinc which might 
otherwise become alloyed with the base, causing small 
holes or pits to appear on its surface, or perhaps the 
occurrence of galvanic action. 



188 PRACTICAL DENTAL METALLURGY. 

Vulcanite is attached to such a base by spurs made 
with a sharp-pointed graver, counter-sunk holes, or 
loops made with a punch along the alveolar ridge. After 
waxing up the denture the base may be varnished to 
protect it from the plaster during vulcanization, after 
which the varnish is removed with alcohol, and the plate 
polished with pumice-stone and whiting, but it cannot be 
well burnished. 

The process of making cast aluminum dentures was 
first introduced by Dr. J. B. Bean of Baltimore, who cast 
the metal through tall conduits lined with clay and 
attached to the gates of his flask, the entire apparatus 
being first heated to an elevated temperature. The pres- 
sure of the column of metal thus produced overcame the 
sluggish flow due to an inherent lack of fluidity and 
lightness of the metal, and forced it into the finer parts 
and irregularities of the mold. 

The cast bases were finally abandoned, because of cor- 
rosion and decomposition. 

Dr. C. C. Carroll, following the efforts of Dr. Bean, 
has devised an apparatus by which very 6ne castings of 
aluminum may be secured through the agency of pneu- 
matic pressure. 

To control shrinkage he has alloyed the aluminum 
slightly so that it can be cast directly on the teeth. 

He gave the writer the following as the composition of 
his two bases: 

Base No. 1 for superior dentures, to be cast under pressure. 

Aluminum 98 per cent. 

Platinum ) 

Silver V 2 " " 

Copper J 

Specific gravity, 2.5; fusing point, 1300° F. 



ALUMINUM. 189 



Base No. 2 is composed of aluminum, tin, copper, and silver; 
specific gravity, 7.5; fusing point, 700° F. This is intended for 
lower dentures, and is cast without pressure,* 

The alloy is melted in a specially constructed plumbago 
crucible, which has the general form of a thick-walled 
cylinder, closed at one end t which serves as a bottom. 
"A channel is formed within the wall of the crucible, 
one orifice of which terminates within the crucible at the 
side and close to the bottom. Starting from this orifice, 
the channel rises in the crucible wall to near the top, 
making a sharp return upon itself, and descends in a 
parallel course after the manner of a siphon, and makes 
its exit at the base and near the side of the crucible. 
Here it terminates in an iron nipple that fits into a cor- 
responding socket in the gateway of the molding-flask. 
A cylindrical plug of soapstone, which fits the open 
mouth of the crucible, is provided with a central tube of 
brass, to the free end of which is, connected by a short 
length of rubber tubing, a large rubber bulb. When the 
metal has been brought to a state of fusion and the cruci- 
ble connected by means of the iron nipple at its base with 
the gateway of the flask, which has been previously 
heated to near redness, the soapstone plug is inserted in 
the mouth of the crucible and the rubber bulb is steadily 
but forcibly compressed. The atmospheric pressure 
forces the fluid metal out through the siphon-like chan- 
nel and into the minutest lines of the mold, yielding a 
fine casting; but in this, as in Bean's process, the con- 
traction of the metal on cooling almost invariably causes 
fracture of the teeth, or the shrinkage will show itself in 
portions of the plate, causing objectionable, or at least 
unsightly, defects/' 

* Prof. C. Iy. Goddard. 



190 PRACTICAL DENTAL METALLURGY. 

Carroll's improved crucible, made of iron and lined 
with asbestos-fiber, is somewhat funnel-shaped, and pro- 
vided with a screw-cut stem, which is pierced by a small 
hole. The flask-gate is also screw-cut to receive the stem 
of the crucible, thus making an air-tight joint. The 
flask and crucible thus attached are placed in a gas- 
furnace, so constructed that a greater heat is applied to 
the crucible than to the flask. When the aluminum is 
melted, the crucible cover, made of iron and lined with 
asbestos-fiber, is clamped on. The cover is also perfor- 
ated by a small hole passing through a nipple, or stem, 
projecting from its outer surface. A bulb is connected 
with this stem by a flexible rubber tube, and by its use 
the requisite amount of pneumatic pressure is secured to 
force the molten aluminum into the mold. 

Dr. Carroll also made a foil of aluminum, of which 
Dr. Dwindle* said: "It is easily worked, crimped, 
folded, twisted into coils, or shaped into pellets, and 
treated like other foil; that it is subject to varying tem- 
pers obtained by annealing, and has the advantage that 
it approaches the color of the teeth more nearly than any 
other metal." 

Bridges are cast similarly to the making of cast plates, 
and seamless crowns, as those of gold, are prepared by 
swaging. Thinly rolled aluminum makes a very ser- 
viceable matrix in filling. 

THE COMPOUND WITH OXYGEN.— Aluminum 
oxide, Alumina, the Sesquioxide of Aluminum, A1 2 3 , 
is found crystallized in hexagonal prisms in nature, as 
ruby, sapphire, corundum,f etc., colored by admixtures. 

* Dental Cosmos, Vol. XXXI, p. 655. 

f Chemical formulae of some of the oxides of aluminum: 

Corundum (Ruby and sapphire the same) Al 2 O s . 

Garnet (CaMgFeMn) 3 Al 2 Si 3 12 . 

Cyanite Al 2 Si0 5 . 



ALUMINUM. 191 



It may be prepared by treating a solution of alum with 
an excess of ammonia, by which an extremely bulky, 
white, gelatinous precipitate of aluminum hydrate is 
formed. This is washed, dried, and ignited to whiteness. 
Thus obtained, alumina constitutes a white, tasteless 
feebly basic coherent mass, very little acted upon by 
acids, and fusible in the oxyhydrogen flame. Emery is 
impure corundum, containing iron and aluminum oxides, 

Feldspar is regarded as the double silicate of po- 
tassium and aluminum, and as having the formula 
A1 2 3 .K 2 0.6Si0 2 . It is much used in the preparation of 
bodies, frits, and enamels for the manufacture of porcelain 
teeth. 

Kaolin is known as a hydrated silicate of aluminum, 
(2A1 2 3 .3Si0 2 ) + 3H 2 0, and is the purest form of clay. 
It is much used in the preparation of bodies for the man- 
ufacture of porcelain teeth. 

ACTION OF ACIDS AND ALKALIS ON ALUM- 
INUM. — Sulphuric acid, concentrated and boiling, dis- 
solves aluminum, but it is not soluble in the dilute acid. 

Nitric acid does not affect aluminum. 

Hydrochloric acid, hot or cold, readily dissolves it, 
forming aluminum chloride, and evolving hydrogen — 

2Al+6HCl=Al 2 Cl 6 -f-H 6 . 

In Potasshrm or sodium hydrate it is soluble, forming 
aluminates and liberating hydrogen — 

Al+3KHO=K 3 A10 3 +H 3 . 

ALLOYS. — Aluminum alloys with nearly all metals, 
except lead; indeed, the wonderful alloys it is capable of 
producing gives it, perhaps, its greatest value. 

Aluminum may be melted in a graphite crucible without 
flux, but great care must be taken not to heat it too hot. 
On account of its high specific and latent heat, alumi- 



192 PRACTICAL DKNTAI, METAUJJRGY. 

num requires a long time to melt; but, unlike some other 
metals, it soon becomes fluid after the melting point is 
reached. 

With mercury alone aluminum is said to form an unsta- 
ble amalgam. A series of dental-amalgam alloys of alumi- 
num are prepared by Dr. Carroll of which it is claimed 
that: the amalgams made of them set quickly, do not 
shiink, and make a dense, fine-grained filling of white 
luster nearer the color of the teeth than any other mate- 
rial; that they do not tarnish nor change color from wear 
and have a strong, tough edge, that will not break by 
burnishing or mastication. 

The experiments made by Dr. Black recently showed 
aluminum in the proportion of 1 to 5 per cent, in silver-tin 
amalgam alloys to so increase the expansion in amalgams 
made of them as to exclude this metal as a component 
in dental-amalgam alloys. 

Gold and aluminum unite, forming a hard and brittle 
alloy. One per cent, of aluminum in gold destroys the 
ductility of the noble metal and gives it a greenish cast; 
5 per cent, of aluminum with gold yields an alloy brittle 
as glass, and 10 per cent, of aluminum produces a white, 
crystalline, and brittle alloy. 

Nurnberg gold, an alloy, for cheap goldware, very 
much resembling gold, and unchanged in air, is com- 
posed of aluminum 7.5, gold 2.5, and copper 90 parts. 

Silver and aluminium readily unite, forming alloys of 
beautiful whiteness, and unchangeable on exposure to 
air. Their hardness is considerably greater than alumi- 
num, but they are more easily worked. An alloy of 100 
parts of aluminum and 5 parts of silver differs but little 
from pure aluminum, save that it is considerably harder 
and takes a beautiful polish. An alloy of aluminum 169 
parts and silver 5 parts possesses considerable elasticity, 



ALUMINUM. 193 



and has been recommended for watch springs, dessert 
' and fruit knives. Equal parts of the two metals pro- 
duce an alloy equal to that of bronze in hardness. 

Copper and aluminum form some exceedingly impor- 
tant alloys, differing according to the quantity of alumi- 
num they contain. Those of a small content of copper 
cannot be used industrial^. With 60 to 70 per cent, of 
aluminum they are very brittle, glass-hard, and beauti- 
fully crystalline. With 50 per cent, the alloy is quite 
soft ; but under 30 per cent, of aluminum the hardness 
returns. The usual alloys are 1, 2, 5, and 10 per cent, 
of aluminium. These are known as aluminum bronze. 
The 10 per cent, bronze is a bright golden, and keeps its 
color and polish in air; it may be easily engraved, shows 
a greater elasticity than steel, and can be easily soldered 
with 20-carat gold solder. When first made, it is brittle, 
acquiring its best qualities after three or four meltings, 
after which it may be melted several times without sensi- 
ble change. It casts well in sand molds, but shrinks 
greatly. It has a specific gravity of 7.68, about equal to 
soft iron. Its strength when hammered will equal that 
of the best steel. Annealing makes it soft and mal- 
leable. It does not clog a file, and may be drawn into 
wire. It melts at about 1700° F. 

Aluminum bronze as a base for artificial dentures: " In 
the proportion of aluminum 100 and copper 900 it oxi- 
dizes but superficially in the mouth, and is as strong and 
resistant to attrition as 18-carat gold; it may be swaged 
as easily as 20-carat gold, but it must be annealed fre- 
quently, and it is necessary to carry the heating almost 
to whiteness, for if the bronze be merely heated until it 
assumes a dark-red color it remains as hard as before." 
(Prof. Souer.) 



194 PRACTICAL DENTAL METALLURGY. 

The alloys of copper and aluminum are prepared in 
the Cowles' electric furnace by fusing together the oxides 
of aluminum and metallic copper with enough carbon 
and flux to reduce them. The oxides and all to be as 
finely divided as possible. 

Solders. — The following alloys may be used as solders 
for articles of jewelry made of 10 per cent, aluminum 
bronze: 

HARD SOLDER. 

Gold 88.88 per cent. 

Silver 4.68 " 

Copper 6.44 " " 

MEDIUM HARD SOLDER- 

Gold 54.40 per cent. 

Silver 27.00 " " 

Copper 18.00 " " 

Mr. Wm. Frismuth of Philadelphia recommends the 
following solders for aluminum, with vaseline as the flux: 

SOFT SOLDER. 

Pure Block Tin from 90 to 99 parts. 

Bismuth < 10 " 1 

HARD SOLDER. 

Pure Block Tin from 98 to 90 parts. 

Bismuth " 1 " 5 

Aluminum " 1 " 5 " 

Schlosser recommends the following for dental labora- 
tory use: 

PLATINUM-ALUMINUM SOLDER. 

Gold 30 parts . 

Platinum 1 " " 

Silver 20 " 

Aluminum 100 ' ' 

GOLD-ALUMINUM SOLDER. 

Gold 50 parts . 

Silver 10 " 

Copper 10 " 

Aluminum 20 " 



ALUMINUM. 195 



O. M. Thowless has patented the following solder for 

aluminum and method for applying it: 

Tin 55 parts . 

Zinc 23 " 

Silver . .. 5 " 

Aluminum 2 " 

First melt the silver and aluminum together then add 
the tin and zinc in the order named. The surfaces to be 
soldered are immersed in dilute caustic alkali or a cyanide 
solution, and then washed and dried. They are next 
heated over a spirit lamp, coated with the solder, and 
clamped together; small pieces of solder being placed at 
the points of union, the whole is then heated to the 
melting point. No flux is used. The following are use- 
ful as solders. 

i. ii. in. 

Zinc 80 parts 85 parts 92 parts 

Aluminum 20 " 15 " 8 " 

The flux used in soldering is composed of 3 parts 
balsam of copaiba, 1 part Venetian turpentine, and a 
few drops of lemon juice. The soldering iron is dipped 
into the mixture. So far, the soldering of aluminum in 
the dental laboratory is very difficult and unsatisfactory. 

Another solder for aluminum, recommended by the 

Scientific American, is composed of the following: 

Cadmium 50 parts. 

Zinc 20 " 

Tin 30 " 

The zinc is first melted in a suitable vessel; then the 
cadmium is added, and then the tin, in small pieces. 

The proportions of the various ingredients may be 
varied, in accordance with the use to which the article is 
put. For instance, when a strong and tenacious solder- 
ing is required, a larger proportion of cadmium can be 
used; where great adhesion is desired, a large propor- 



196 PRACTICAL DENTAL METALLURGY. 

tion of zinc should be used, and where a nice and durable 
polish is desired, a greater per cent, of tin should be used. 

An alloy of zinc, copper, and aluminum has been intro- 
duced as a dental base. (See also Carroll's alloys for 
cast dentures, pp. 188 and 189.) It is said to be unaffected 
by the oral fluids. 

Tin and aluminum form alloys little affected by acids. 
With 100 parts aluminum and 10 parts tin an alloy is 
produced much whiter than alluminum and but little 
heavier. It can be welded and soldered like brass. 

Iron and aluminum unite readily. Ostberg, a Swedish 
inventor, discovered that an exceedingly small content 
of aluminum (5-1000th of 1 per cent.) in wrought iron 
served to lower its fusing point about 500° F., so that 
castings may be made from it as readily as from the 
highly carburized cast iron. Iron may be coated with 
aluminum much as it is with tin. 

Zinc and aluminum unite to form alloys very useful 
for soldering the latter. They are prepared by first melt- 
ing the aluminum and adding the zinc gradually, after 
which some fat is introduced to prevent oxidation, and 
the alloy is stirred rapidly with an iron rod. Aluminum 
may be frosted by immersion in a solution of potassa. 

TESTS FOR ALUMINUM IN SOLUTION.— 
Sulphuretted hydrogen does not produce a precipitate 
when added to a solution of a salt of aluminum. 

Ammonium hydro-sulphide produces a white pre- 
cipitate of aluminum hydrate and evolves sulphuretted 
hydrogen. 

Ammonium hydrate throws down a bulky, gelatinous 
aluminum hydrate, slightly soluble in the precipitant. 

BLOW-PIPE ANALYSIS.— Compounds of alumi- 
num are not reduced to the metal, but most of them are 
reduced to the earth, by ignition on charcoal. If this 



ALUMINUM. 197 



residue is moistened with a solution of cobalt nitrate, 
and strongly ignited, it assumes a blue color. Silica 
gives the same reaction, but the color is paler and thus 
distinguished. 

ELECTRO-DEPOSITION OF ALUMINUM.— 
Jeancon patented a process for depositing aluminum from 
an aqueous solution of a double salt of that metal and 
potassium, by means of a current from three Bunsen's 
cells, the solution being at 140° F.* 

In order to plate aluminum it must first be coated with 
copper. 

* Telegraphic Journal, Vol. 1, p. 308. 



CHAPTER XV. 
MERCURY. 

Hydrargyrum. Symbol, Hg. 

Valence, II, (Hg 2 ) n . Specific gravity, 13.595. 

Atomic Weight, 199.71. Malleable at -39° C. 
Melting point, -39° C. 
Boiling point, 357.3° C. 
Conductivity (heat), greater Conductivity (electricity), ^ 7 th 

than water. of silver. 

Specific heat, 0.0333. Chief ore, cinnabar. 

Color, silver- white. Crystals, octathedral at — 39° C. 

OCCURRENCE. — Mercury occurs in nature chiefly 
as the red sulphide, HgS, cinnabar, which, as a rule, is 
accompanied by more or less of the reguline metal. The 
most important mercury mines of Europe are those of 
Almaden, Spain, and of Idria, in Illyria; it is also found 
in China, Mexico, Corsica, Peru, and California. The 
European mines, until lately, furnished the bulk of the 
mercury of commerce, but they have been eclipsed by the 
rich deposits of New Almaden, near San Jose, California. 
The mines of the latter have been the most productive in 
the world, yielding more than 3,000,000 pounds annu- 
ally, and large quantities are still taken from them. The 
ore of old Almaden is of a dull red color in mass; of a 
dull brick-red color when in fine powder, and is of 3.6 
specific gravity. That from New Almaden is of a bright 
red color, slightly inclining to purple, and not so hard as 
the Spanish ore; of a bright vermilion color in powder, 
having a specific gravity of 4.4. The California cinnabar 
is richer in mercury, because purer, than the Spanish, 
the former yielding about 70, the latter about 38 per 
cent, of mercury. 



MERCURY. X99 



Mercury is also found jree; forming an amalgam with 
silver; and in the form of protcchloride (native calomel). 

REDUCTION.— The metal is obtained almost exclu- 
sively from the sulphide or native cinnabar, arid is 
extracted by two principal methods. By the first method 
the mineral is picked, crushed, and mixed with lime. 
The mixture is then introduced into cast-iron retorts, 
which are placed in rows, one above the other, in an 
oblong furnace, and connected with earthenware receiv- 
ers, one-third full of water; heat is applied, the lime 
combines with the sulphur, forming the sulphide and 
sulphate of calcium — 

4HgS + 4CaO=3CaS + CaS0 4 + Hg 4 , 

while the mercury distills over, and is condensed in the 
receivers. In the second method the decomposition of 
the cinnabar is effected by the direct exposure of the ore 
lo the oxidizing flame of the furnace, and the mercury 
vapor is recovered in more or less imperfect condensers. 

PURE MERCURY.— The commercial article, as a 
rule, is quite pure chemically, and only needs to be 
forced through chamois skin to be fit for ordinary pur- 
poses; but it frequently contains foreign metals, as lead, 
tin, zinc, and bismuth. It is seldom intentionally adul- 
terated. When impure, the metal has a dull appearance, 
leaves a trace on white paper, is deficient in due fluidity 
and mobility, as shown by its not forming perfect 
globules, is not totally dissipated by heat, and, when 
shaken in a glass bottle, coats its sides with a pellicle, 
or, if very impure, deposits a black powder; if agitated 
with strong sulphuric acid, the adulterating metals be- 
come oxidized and dissolved, and thus the metal may be 
to a limited extent purified. If sulphuretted hydrogen 
does not act upon hydrochloric acid, which has been 



200 PRACTICAL DENTAL METALLURGY. 

previously boiled upon the metal, the absence of contam- 
inating metals is shown. 

Detection of Lead. — Lead may be detected by 
shaking the suspected metal with equal parts of acetic 
acid and water, and then testing the acid by sulphate of 
sodium, or iodide of potassium. The former will pro- 
duce a white, the latter a yellow, precipitate, if lead be 
present. 

Detection of Bismuth. — Bismuth is discovered by 
dropping a nitric solution of the mercury, prepared with- 
out heat, into a quantity of distilled water, when the 
sub-nitrate of bismuth will be precipitated. 

Detection of Tin. — Complete solubility of the metal 
in nitric acid shows the absence of tin. 

Lead is the chief impurity, and may be removed by 
exposing a thin layer of the metal to the action of nitric 
acid diluted with twice the quantity of water, which 
should well cover the surface, remaining for a day or two, 
with frequent stirring. The lead is much more easily 
oxidized and dissolved than the mercury, though some 
of the latter also passes into solution. The mercury is 
afterwards well washed with water, and dried first with 
blotting paper, then by gentle heat. At the same time 
most of the other metallic impurities are removed. Mer- 
cury is, however, best purified for dental use by redistil- 
lation. 

Chemically pure mercury may be obtained by decom- 
posing pure mercuric oxide by heat, and washing the 
condensed metal with dilute nitric acid. 

EXPERIMENT No. 46.— Into a test-tube containing equal parts of 
acetic acid and water, drop some mercury, suspected to contain lead, and 
shake thoroughly. Add a solution of potassium iodide — yellow precipitate if 
lead is present. 

EXPERIMENT No. 47.— Dissolve a little mercury, suspected to con- 
tain bismuth, in nitric acid, without heat. Drop into considerable quantity 
of distilled water — white precipitate if bismuth is present. 



MERCURY. 201 



EXPERIMENT No. 48.— Dissolve mercury, suspected to contain tin, in 
nitric acid. If tin is present, a white, flaky residue, oxide of tin, remains. 

EXPERIMENT No. 4 9.— Boil mercury, suspected of containing metallic 
impurities, in hydrochloric acid, decant the acid, and add to it sulphuretted 
hydrogen. If no action, the absence of contamination is shown, 

EXPERIMENT No. 50. — Roll impure mercury over a white paper or 
clean watch glass: a "tail" is left where it passes. 

PROPERTIES. — Mercury, or quicksilver, as it is often 
called, is of a silver-white color, liquid at ordinary tem- 
perature — above- 39° C. — odorless and tasteless. Vol- 
atile at common temperature (see experiment No. 51), 
but more rapidly volatilizes as the temparature increases, 
and at 357.3° C. it boils, being finally volatilized without 
residue. When globules are dropped upon white paper 
they should roll about freely, without tailing, retaining 
their globular form. It should be perfectly dry, and 
present a bright surface. When perfectly pure it under- 
goes no alteration by the action of the air or of water, 
but in the ordinary state it suffers a slight tarnish. It 
solidifies with considerable contraction into a compact 
mass of regular octahedra, which can be cut with a knife, 
or flattened under the hammer. 

EXPERIMENT No. 51.— In a small vial containing a little metallic 
mercury, suspend a strip of gold-foil about a quarter of an inch over the metal. 
In a short time the lower portion of the gold will become white, owing to the 
condensation of the mercury upon it. 

EXPERIMENT No. 52.— On a clean strip of copper place a globule of 
mercury; the latter soon covers a considerable surface, giving it a white 
color. Heat the copper, and the original color will be restored, the mercury 
volatilizing. 

USES. — It is in constant requisition in the chemical 
laboratory, and is greatly used in the construction of 
thermometers, barometers, and manometers, for the de- 
termination of the capacity of vessels, and for many other 
purposes. 

In medicine, in the uncombined state, it is inert, but 
in combination acts as a peculiar and universal stimu- 



202 PRACTICAL DENTAL METALLURGY. 



lant. When exhibited in the finely divided state it 
forms several preparations, producing peculiar effects; 
this fact, however, does not prove that the uncombined 
metal is active, but that in minute division it is favorable 
to chemical action and combination. Rubbed up with 
chalk, mercury forms hydrargyrum cum creta; with the 
confection of roses and licorice, massa hydrargyri; with 
lard and suet, unguentum hydrargyri. 

Mercurial poisoning, ptyalism, salivation, is first ob- 
servable by a coppery taste, a slight soreness of the gums, 
and an unpleasant sensation in the sockets of the teeth, 
when the jaws are firmly closed. 

In dentistry mercury is used to form alloys known as 
amalgams. (See chapter on Amalgams.) 

COMPOUNDS WITH OXYGEN.— Monoxide or 
Mercuric Oxide HgO, perhaps more commonly known 
as red oxide of mercury, or red precipitate. The 
compound may be prepared by several methods, the 
most prominent of which are: First, by exposing 
mercury in a glass flask with a long, narrow neck, for 
several weeks, at a temperature of about 315° C. The 
product of such exposure and heat is highly crystalline 
and of a dark red color. Second, as it is generally pre- 
pared, by cautiously and thoroughly heating any of the 
mercuric or mercurous nitrates to complete decomposi- 
tion, which latter fact is recognized by the absence of 
the characteristic red fumes and odor of nitrous oxide. By 
this means the acid is decomposed and expelled, oxidiz- 
ing the metal to the maximum if it happens to be in the 
state of mercurous salt. The product thus obtained is 
also crystalline and very dense, but of a much paler color 
than the preceding. While hot, it is nearly black. 
Third, by adding caustic potash in excess to a solution 
of mercury chloride, by which a bright yellow precipi- 



MERCURY. 203 



tate of mercuric oxide is thrown down. This precipitate 
is destitute of crystalline character, and much more 
minutely divided than the two preceding. 

The monoxide is only slightly soluble in water, com- 
municating to the latter an alkaline reaction and metallic 
taste; it is highly poisonous. When strongly heated, it 
is decomposed into mercury and oxygen gas. 

EXPERIMENT No. 53.— In a test-tube place a small quantity of mer- 
curic oxide and close by rubber stopper, through which pass a glass tube 
connected with rubber tubing. Place mouth of the tube below the surface ot 
water and heat test-tube to dull-redness. The oxygen separates from the 
mercury and escapes bubbling through the water, while the mercury con- 
denses in a ring upon the colder part of the test-tube. 

HgO = Hg+0. 

Mercurous Oxide, Hg 2 0; Suboxide or Gray Oxide of 
Mercury may be prepared by adding caustic potash to 
mercurous nitrate. It is a dark gray, nearly black, 
heavy powder, insoluble in water, slowly decomposed by 
the action of light into metallic mercury and the red 
oxide. 

ACTION OF ACIDS ON MERCURY.— Hydro- 
chloric acid does not attack mercury. 

Sulphuric acid, boiling, converts it into mercurous 
sulphate, liberating sulphur dioxide. 

Nitric acid is the most effective solvent for mercury. 
It dissolves readily in the dilute acid with heat, or in 
the cold, if nitrous acid is present; with the strong acid, 
heat is soon generated, and with considerable quantities 
of the material the action acquires an explosive violence. 
At ordinary temperatures, dilute nitric acid, when ap- 
plied in slight excess, produces chiefly normal mercu- 
rous nitrate, but when the mercury is in excess, more or 
less of basic mercurous nitrate is formed; hot dilute 
nitric acid, in excess, forms chiefly mercuric nitrate; 
when the mercury is in excess, both basic mercurous and 



204 PRACTICAL DENTAL METALLURGY. 

basic mercuric nitrates are formed. In all cases, chiefly 
nitric oxide gas is evolved. 

ALLOYS. — Mercury unites readily with most metals 
except iron and platinum. With the former it has been 
found to unite only indirectly; for example, by rubbing 
very finely divided iron with mercuric chloride, water, 
and a few drops of metallic mercury. The latter metal 
can only be combined in the spongy state. Yet both of 
these metallic elements combine chemically with mercury 
to form definite compounds, according to Bloxam and 
other authorities, and present the composition, FeHg 
and PtHg 2 respectively. 

Of gold and mercury, Dr. H. H. Burchard,* in an 
exceptionally able paper, quotes: 

"A gold amalgam 1 to 1000 has all the fluid mercury 
expressed through chamois; the residue treated with 
dilute nitric acid at a moderate heat. A solid amalgam 
is left, Au 8 Hg, which crystallizes in four-sided prisms, 
and does not melt even when heated until the mercury 
volatilizes. "f And further, "A mixture of gold and 
mercury was heated to a temperature a little above the 
boiling-point of mercury, and the heat maintained until 
the weight became constant, and there resulted an amal- 
gam containing 10.3 per cent, of mercury, giving a for- 
mula of Au 9 Hg." (Hiorns.) 

Then adds: " Guettier points out that a saturated 
solution of gold in mercury is Au 2 Hg, a mass of 
waxy consistence. Evidently, when the gold exceeds 
this ratio, there is not a perfect chemical compound, as, 
for instance, in the Au 8 Hg amalgam." 

Silver and mercury combine very readily, and undoubt- 
edly form a definite chemical compound. Joule gives its 

* Dental Cosmos, Vol. XXXVII, p. 989. 

f T. H. Henry, Philos. Mag., Vol. IX, p. 468. 



MERCURY. 205 



formula as Ag 2 Hg, Bloxaru as Ag 2 Hg 3 . It also forms 
two native amalgams, having the formulae of AgHg and 
Ag 2 Hg 6 . 

With copper, zinc, tin, and lead it also forms definite 
chemical compounds, and their formulae may be expressed 
respectively as: CuHg,Zn 2 Hg, Sn 2 Hg, and Pb 2 Hg. The 
conclusion, then, is obvious that our dental amalgams 
are probably mostly — fundamentally, at least — chemical 
compounds, but usually with mercury, and, perhaps, 
some other constituent in excess. 

EXPERIMENT No. 54. — Throw a piece of clean sodium upon warm, 
dry mercury; union takes place with incandescence and evolution of heat 
sufficient to volatilize portions of the metals. 

EXPERIMENT No. 55.— Repeat the experiment, using potassium, 
instead of sodium: the combination is attended with even more violence. 
An amalgam is formed with the metal in each instance. 

VERMILION. — Mercuric sulphide, HgS, occurs native 
as cinnabar, a dull-red mineral, the most important ore 
of mercury. It may be prepared by several different 
methods, much depending upon the purity of the mate- 
rials employed. When mercury and sulphur are heated 
together the union is accompanied with much energy, 
and if the product be sublimed, becomes the red or mer- 
curic sulphide. The sulphur is best first melted and the 
mercury gradually added by straining through linen 
cloth, whereby it falls in a minutely divided state, while 
the mixture is constantly stirred. When the tempera- 
ture arrives at a certain point, the combination takes 
place suddenly with a slight explosion, attended with the 
inflammation of the sulphur, which must be extinguished 
by covering the vessel. The product of the combination 
is a black mass, generally containing an excess of sul- 
phur, which, before the sublimation is performed, should 
be gotten rid of by gentle heat on a sand-bath. Sub- 
limation is best carried on in a closely stopped glass 



206 PRACTICAL DENTAL METALLURGY. 

matrass, which should be placed in a crucible contain- 
ing sand, and, thus arranged, exposed to a red heat. 
The resulting vermilion is reduced to a fine powder by 
levigation, the beauty of the tint depending much upon 
the extent to which the division is carried. 

It is prepared in a wet way by intimately mixing 100 
parts of mercury with 38 parts of the flowers of sulphur, 
and the iEthiop's mineral digested, with constant agita- 
tion, in a solution of 25 parts of caustic potash in 150 
parts of water at 45° C. (the water lost by evaporation 
being constantly replaced), until the preparation has 
come up to its maximum of fire and brilliancy, which 
takes a good many hours. Purely sublimed vermilion 
has a comparatively dull color, and must be manipulated 
with an alkaline (potassium) sulphide solution to give it 
the necessary fire. The action of the alkaline sulphide 
consists probably in this, that it dissolves successive in- 
stallments of the amorphous preparation and redeposits 
them in the crystalline form. 

Properties. — It is a fine, bright scarlet powder, per- 
manent in air, odorless and tasteless, insoluble in water, 
alcohol, dilute nitric, concentrated hydrochloric, or sul- 
phuric acids. Nor is it acted upon by boiling potassium, 
hydrate, sulphide of ammonium, cyanide of potassium 
or sulphite of soda. It is slightly acted upon by concen- 
trated hot nitric acid, and completely soluble in a solution 
of potassium sulphide in the presence of free alkali or a. 
solution of sodium sulphide. Nitro-hydrochloric acid 
decomposes it into mercuric chloride, which is readily 
soluble. It may be completely sublimed, as has been 
seen, without decomposition, but if exposed to a tem- 
perature of 315.5° (600° F.) it is decomposed into 
metallic mercury and sulphur dioxide. It is frequently 
adulterated with red lead, dragon's blood, chalk, ferric 



MERCURY. 207 



oxide, realgar (As 2 S 2 ), and brickdust. If lead be present 
it will yield a yellow precipitate when digested with acetic 
acid and potassium iodide added. Dragon's blood may be 
detected by alcohol, which will take up the coloring 
matter of that substance if present. Chalk is detected 
by an effervescence on the addition of an acid. Most 
other impurities may be detected by subliming a small 
portion of the compound. The non-volatile substances 
used for adulteration will remain behind. 

Uses. — When pure it is much used as a pigment, on 
account of its brilliancy and color. Its unalterableness 
and resistance to chemical action render it particularly 
valuable in giving the red color to vulcanizable rubber 
used in the construction of artificial dentures of red and 
pink vulcanite in the composition of which it forms, in 
some cases, about one-third of the entire weight of the 
compound. Notwithstanding the poisonous character of 
mercurial compounds in general, and the frequency of 
troubles of an inflammatory nature of the mucous mem- 
brane in mouths fitted with rubber dentures, it is obvi- 
ously very improbable, when we consider the properties 
of pure vermilion, that such conditions can be in any 
degree attributable to the presence of this substance 
per se. It is quite possible that impure vermilion may 
contain from the start free mercury; be contaminated 
with arsenic bisulphide, or poisonous adulterations. 
Again, the practice of dissolving tin-foil off of the surface 
of plates with nitro-hydrochloric acid just after vulcan- 
ization may possibly decompose some little vermilion, 
forming soluble bichloride. It is highly improbable that 
any of these conditions can be found, yet it is possible. 
It is said that free mercury has been observed with the 
microscope in finished vulcanite. The occurrence of oral 
inflammatory conditions, under black rubber dentures, 



208 PRACTICAL DKNTAI, METALLURGY. 

precisely similar to those under red rubber, practically 
relieves vermilion of the responsibility. Such inflamma- 
tory troubles are directly attributable to its rough and 
porous surface, lack of cleanlijiess on the part of the 
wearer, and the fact that rubber, being a non-conductor of 
heat, not only prevents proper radiation from the muc- 
ous membrane, but also prevents this membrane being 
cooled by the passage of air, fluids, or foods through the 
mouth. 

EXPERIMENT No. 56.— Test vermilion and red rubber (pieces and 
filings) in nitric, hydrochloric, sulphuric, and nitro-hydrochloric acid. 

EXPERIMENT No. 57.— Prepare red rubber and vermilion and examine 
under microscope. 

TESTS FOR MERCURY IN SOLUTION.— Sul- 
phuretted hydrogen, gradually added to mercuric solu- 
tions, forms at first a white precipitate; by further addi- 
tions of the reagent, the precipitate becomes yellow- 
orange, then brown, and finally black. Such progressive 
variation of color is characteristic of mercury. With 
mercurous compounds, sulphuretted hydrogen, and solu- 
ble sulphides precipitate mercurous sulphide, Hg 2 S, black, 
without change of color. 

Soluble Iodides precipitate mercuric iodide, Hgl 2 , 
from mercuric compounds, first reddish-yellow, then red. 
From mercurous solutions they precipitate mercurous 
iodide, Hg 2 T 2 , greenish-yellow in color. 

Caustic soda or potassa precipitates yellow mercuric 
oxide from mercuric salts, and black mercurous oxide 
from mercurous salts. 

Ammonium hydrate throws down a "white precipi- 
tate" of mercuric chloramide (H 2 NHgCl) from mercuric 
salts, but black precipitates are thrown down from mer- 
curous salts. 

EXPERIMENT No. 58.— The student should perform these tests. 



MERCURY. 209 



BLOW-PIPE ANALYSIS.— All compounds of mer- 
cury, in glass tubes or on charcoal, are quickly volatile 
before the blow-pipe. All compounds of the metal, dry, 
and intimately mixed with dry sodium carbonate, and 
heated in a glass tube closed at one end, give a sublimate 
of metallic mercury as a gray mirror coat on the inner 
surface of the cold part of the tube. 

ELECTRO-DEPOSITION OF MERCURY.— If a 
piece of bright, clean copper be immersed in a solution 
of a mercuric salt acidulated with hydrochloric acid the 
surface will be rendered white by the deposition of 
mercury upon it. 

From solutions of mercuric chloride, cyanide, or 
nitrate, aluminum deposits mercury, forming an amal- 
gam which decomposes water at 60° F., and rapidly 
oxidizes and becomes heated in the air. 

Dr. Kirk's method for preparing copper amalgam: 
" Precipitate the copper directly into the mercury by 
electrolytic process. This may be done conveniently by 
pouring a quantity of mercury into a suitable glass ves- 
sel — a small battery jar, for example — and suspending a 
thick plate of copper, by means of a wooden support, 
some distance above the surface of the mercury. A 
saturated solution of cupric sulphate is then poured into 
the jar until the copper plate is completely submerged. 
The cathode pole of a battery, or other source of electrical 
current, is then connected with the layer of mercury, and 
the anode with the copper plate. All that portion of 
the cathode electrode in contact with the cupric sulphate 
solution should be insulated with gutta percha, and only 
the point, which is in contact with the mercury, left ex- 
posed. The passage of the current causes solution of the 
copper from the anode and deposits it in the mercury 
continuously as long as the foregoing conditions are 



210 PRACTICAL DENTAL METALLURGY. 

maintained. The precipitation should be continued 
until the mercury is saturated, which will be evidenced 
by the appearance of the characteristic red color of the ex- 
cess of copper at the cathode pole. When the saturation 
point has been fully reached, the mass should be washed, 
first in dilute hydrochloric acid, and then in water, dried 
and compressed as is usual with this amalgam when pre- 
pared by the ordinary processes."* 

* Operative Dentistry, IS- C. Kirk, p. 226. 



CHAPTER XVI. 
SILVER. 

Argentum. Symbol, Ag. 

Valence, I. Specific gravity, 10.4. 

Atomic weight, 107.67. Malleability, 2d rank. 
Melting point, 1040° (1904° F.). Tenacity, 4th rank. 

Ductility, 2 rank. Conductivity (electricity), 100. 

Conductivity (heat), 100. Chief ore, silver glance. 

Specific heat, 0.057. Crystals, isometric. 
Color, white. 

OCCURRENCE.— Silver is widely diffused through- 
out the earth's crust. It is found chiefly in the United 
States, Mexico, Peru, and Chile; Austria, Hungary, Nor- 
way and Australia also furnish considerable amounts. 

Of the varieties of silver ores the following chiefly 
are metallurgically important. (1) Reguline silver, (2) 
horn silver, (3) silver glance, (4) silver-copper glance, (5) 
pyraigyrite, (6) stephanite, and (7) polybasite. Silver is 
also frequently met with in base metallic ores, as in lead 
ores and many kinds of pyrites. 

Reguline silver, native silver. Owing to the weak 
affinity of silver for other substances it is frequently 
found free in a metallic state, occurring in flat masses, 
and at times in an arborescent form, composed of numer- 
ous isometric crystals strung' together, or in twisted 
filaments. In the I^ake Superior district it occurs with 
native copper, showing in specks upon the surface of the 
latter metal. With mercury it is found as a native cry- 
stalline amalgam. Native silver is usually free from any 
considerable admixture of other metals, but it always 
contains gold. 

Horn silver, native chloride, AgCl. The ore is 
named from its resemblance to horn in texture aud 






212 PRACTICAL DENTAL METALLURGY. 

appearance. It is of a pearl-gray color when freshly 
cut, and on exposure to sunlight turns brown. It con- 
tains about 75.3 per cent, silver. The corresponding 
bromide and iodide also occur native. 

Silver glance, native sulphide, Ag 2 S, is the most 
important ore of silver. It is a soft, gray, and somewhat 
malleable mineral, may be cut with a knife, is quite 
fusible, and when pure contains 87-1 per cent, silver. It 
is frequently found associated with copper, as silver-cop- 
per glance (AgCu) 2 S; with antimony, as pyrargyrite^ 
Ag 3 SbS 3 , and as stephanite, Ag s SbS 4 , with copper, anti- 
mony, and arsenic, as polybasite, 9(Ag 2 ,Cu 2 )S+(Sb 2 , 
As 2 )S 3 ; with lead, as argentiferous galena, and with iron. 

REDUCTION.— The method by which silver is ex- 
tracted from its ores depends chiefly on the nature of the 
admixtures, the state of the combination of the silver 
being as a rule irrelevant in the choice of process, because 
some at least of the noble metal is always present as sul- 
phide, and the mode of treatment for it includes all other 
forms. 

Amalgamation. — If the ore is comparatively free from 
base metals, amalgamation is resorted to. Most ores con- 
tain too great a proportion of earthy matter, etc., to admit 
of any other method economically, even in localities where 
fuel is plenty. Several methods of amalgamation are 
employed, varying with different localities and circum- 
stances, but the principles involved are similar, and a 
general description will suffice for all. 

The ore is ground and roasted at a dull-red heat with 
common salt, which converts the sulphide of silver into 
chloride — 

Ag 2 S + 2NaCl + 40 from the air=2AgCl + Na 2 S0 4 . 

The mass, along with certain proportions of water, 
scrap-iron, and mercury, is placed in barrels, which are 



SILVER. 213 

made to rotate about their axis, so that the several ingre- 
dients are forced into constantly varying contact with 
each other. The salt solution takes up a small propor- 
tion of the chloride, which in this (dissolved) form is 
quickly reduced by the iron to the metallic state — 

2AgCl+ Fe=FeCl 2 + 2Ag, 

so that there is, so to say, room made in the brine for 
another instalment of silver chloride, which in turn is 
reduced, and so on. The metal, as soon as freed, is 
combined with the mercury in a semi-fluid amalgam, 
which, on account of its specific gravity, is easily sepa- 
rated from the dross. The silver amalgam is then 
pressed in linen or some other suitable cloth bags, to 
separate the amount of comparatively free mercury, 
which, of course, is reused in the process. The remain- 
ing solid amalgam is subjected to distillation from iron 
retorts, the mercury recovered as a distillate, while the 
silver in a more or less impure state remains in the retort. 

The silver furnished by the amalgamating process is 
never pure, even in a commercial way. A general 
method of its purification is to fuse it with lead, and 
subject the alloy to cupellation. Cupel silver is apt to 
contain small quantities of lead (chiefly), bismuth, anti- 
mothy, copper, and more or less gold. The first three 
can be removed by recupellation, without added lead, at 
a high temperature. The gold, if present to the extent 
of 1 per cent, or more, is removed by treating with nitiic 
or sulphuric acid. The copper is allowed to remain, for 
commercial silver. 

Argentiferous Galena. — The lead extracted from 
galena often contains a sufficient quantity of silver to 
allow of profitable extraction. This is accomplished by 
first concentrating the lead and silver alloy by the Pat- 



214 PRACTICAL DENTAL METALLURGY. 

ttnsoti process, which is based upon the fact that the 
alloy of silver and lead has a lower fusing point than 
lead alone, and therefore remains fluid after the purer 
lead crystallizes. Alloys are thus concentrated from lead 
containing not more than 3 or 4 ounces of silver per ton 
to that which contains about 300 ounces to the ton, when 
by cupellation the lead and other oxidizable metals are 
removed as oxides, leaving pure silver. 

Desilvering Lead. — The process is thus described by 
Bloxam: 

"Bight or ten cast-iron pots, set in brickwork, each 
capable of holding about six tons of lead, are placed in a 
row with a fireplace underneath each of them. Suppose 
that there are ten pots numbered consecutively, that on 
the extreme left of the workmen being No. 1, and that 
on his extreme right No. 10. About 6 tons of the lead 
containing silver are melted in pot No. 5, the metal 
skimmed, and the fire raked out from beneath, so that 
the pot may gradually cool, its liquid contents being con- 
stantly agitated with a long iron stirrer. As the crystals 
of lead form, they are well drained in a perforated ladle 
(about ten inches wide and five inches deep) and trans- 
ferred to pot No. 4. When about four-fifths of the metal 
have thus been removed in the crystals, the portion still 
remaining liquid, which retains the silver, is ladled into 
pot No. 6, and the pot No. 5, which is now empty, is 
charged with fresh argentiferous lead, to be treated in 
the same manner. 

" When pots Nos. 4 and 6 have received, respectively, 
a sufficient quantity of the crystals of lead and of the 
liquid part rich in silver, their contents are subjected to 
a perfectly similar process, the crystals of lead being 
always passed to the left and the rich argentiferous alloy 
to the right. As a final result to these operations, the 
pot No. 10, to the extreme right, becomes filled with a 
rich alloy of lead and silver, sometimes containing three 
hundred ounces of silver to the ton, whilst pot No. 1, to 
the extreme left, contains lead in which there is not more 
than one-half an ounce of silver to the ton." 



SILVER. 



215 



Cupellation. — The extraction of the silver from the 
rich alloy of silver and lead is accomplished by a process 
of refining or cupellation, which is based upon the prop- 
erty possessed by certain oxides of being absorbed by the 
porous cupel. The process is necessarily modified accord- 
ing to the quantity of alloy to be cupelled; the principle, 
however, remains identical. 

The cupel, Fig. 33, a small, shallow crucible, so named 
from the diminutive of the L,atin cupa, a cup, is made 

from prepared bone- 
ash, moistened with 
sufficient warm water 
to hold it together. 
Sometimes a little 
wood-ashes or potas- 
sium carbonate is 
added to the water for 
moistening the bone- 
ash. After proper 
Fig. 33. moistening and mix- 

ing the cupel is formed by packing and tamping the 
moistened ash into a steel mold made for the purpose, and 
the cupel knocked out by a gentle tap. The ash should 
not be too fine or packed too densely, or the cupel will 
want in porosity; nor should it be too coarse or too 
loosely packed, resulting in a cupel so porous as to cause 
a loss of the metal. A good cupel, well dried, should 
not crack on being heated, and should be capable of ab- 
sorbing nearly its own weight in lead oxide. 

The furnace used in operations of a small character is 
a muffle furnace, called an assayer's furnace, similar to 
a continuous-gum furnace. The muffle contained is 
identical with that employed for continuous-gum work, 
except that a narrow slit is provided on each side or at 




216 PRACTICAL DENTAL METALLURGY. 

the end, for the circulation of a current of air over the 
cupel. 

The cupel is first heated in the muffle to an even tem- 
perature with the latter, which should be a full red heat. 
The weighed mass of alloy may then be gently placed 
on the cupel, the muffle closed, and the alloy heated to 
redness as soon as possible. When this degree is attained 
the muffle is opened and air admitted. As the air 
strikes the molten mass a film of oxide quickly makes its 
appearance upon its surface, which, waving over the 
melted alloy, is quickly absorbed by the cupel, only to be 
replaced by other oxide, which is also absorbed; this is 
continued, the metallic globule rapidly diminishing in size, 
uutil at last all of the lead has been reduced to an oxide 
and gotten rid of. The operator must carefully watch 
the process during this time, for if the mass becomes too 
highly heated silver will be lost by volatilization, and if 
insufficient heat is maintained, the mass freezes, and the 
proper temperature cannot be restored without loss of 
noble metal. A proper temperature is maintained by 
observing the color of the muffle and cupel, the former of 
which should be reddish-white, and the latter full red, the 
molten alloy will then appear luminous and clear, and 
fumes of oxide will be seen whirling over the mass. 
When the last of the lead has been oxidized and gotten 
rid of, the metallic globule remaining is observed to 
rapidly revolve on its axis, is covered with iridescent 
tints, and later assumes an exceedingly bright appear- 
ance, which is technically termed brightening or corusca- 
tion of the button. When this is observed the temperature 
should be somewhat increased to insure the expulsion of 
the last traces of lead. When the operator is assured that all 
the lead has been expelled the button is allowed to slowly 
cool to prevent spitting, sputtering or vegetatio?i of the 



SILVER. 217 

mass, resulting in a loss of some of the silver. Remov- 
ing the lead, however, is not the only action; if it were, 
little would be gained in the process. Another action 
goes on whilst the lead is being oxidized in a current of 
air, and other metals, except gold and silver, are also 
oxidized and carried off with the litharge. If the lead 
is therefore properly proportioned the resulting button 
will consist of silver and gold, if the latter was present 
originally. Any gold present may be recovered by the 
parting process. (See chapter on Gold.) 

EXPERIMENT No. 59.— If the metallurgical laboratory contains an 
assay furnace or a muffle furnace that can be used as such, the instructor 
should cupel a small button of silver for the demonstration of the process. 

CHEMICALLY PURE SILVER in small quantities 
may be easily prepared in the laboratory by dissolving 
commercial or coin silver in pure dilute (50 per cent.) 
nitric acid contained in a Florence flask, hastening the 
action by gently heating over a sand-bath. After the 
silver has been dissolved, and the solution somewhat 
cooled, add an equal bulk of distilled water, and filter 
into a second flask. To the filtrate add a saturated 
solution of sodium chloride (common salt) until no more 
white precipitate of silver chloride is formed — 

AgN0 3 + NaCl=AgCl + NaN0 3 . 
The flask should then be stopped and shaken for sev- 
eral minutes, when, on being allowed to rest, the chlcride 
will quickly fall to the bottom, leaving a clear, super- 
natant liquid above, which, if copper be present, will be 
colored a bluish-green. If to this clear supernatant 
liquid the salt solution be added, the operator is enabled 
to determine instantly whether all of the silver has been 
thrown down as the chloride, or not. If so, the clear 
liquid is decanted off and the chloride washed until the 
wash-water does not assume the slightest tinge of blue 



218 PRACTICAL DENTAL METALLURGY. 

upon the addition of ammonia. The chloride is now 
best transferred to a beaker, or some other wide-mouthed 
vessel, and about twice its bulk of water, acidulated with 
about 10 per cent, of sulphuric acid, added. Several 
small pieces of iron in some form, preferably lath-nails, 
may now be added to the mixture, and the whole stirred 
with the closed end of a test-tube. The following 
reactions then take place, during which ferrous sulphate 
and hydrochloric acid are formed and silver liberated, 
thus — 

Fe+H a S0 4 =FeS0 4 +H 2 , and 

2H + 2AgCL=2HCl+2Ag. 

The completion of the reaction is recognized by the 
changing of the precipitated mass from white to a dark- 
gray, which is the color of the finely divided silver. The 
small pieces of iron are now removed, the precipitated 
silver washed and rewashed with dilute hydrochloric 
acid, then with distilled water, dried, mixed with about 
an equal bulk of potassium carbonate, and melted in a 
well-boraxed crucible. 

EXPERIMENT No. 60.— The student should refine a silver dime, or an 
equal weight of silver, by the above means, obtaining the pure silver in its 
stead. 

Pure Silver Nitrate Crystals or pure Silver may 
be prepared by digesting commercial, or coin silver, in 
nitric acid as before, and evaporating the solution over a 
sand-bath. After the water and free acid is driven off a 
greenish solid of silver and copper nitrates remains. By 
continued heat the former is fused and the latter is 
changed to black oxide of copper, CuO, by driving off 
the nitrogen tetroxide (or dioxide, at high temperatures, 
N0 2 ). When the evaporating dish has sufficiently 
cooled to be handled, a small quantity of distilled water 
is added and the contents of the dish stirred and then 



SILVER. 219 

filtered; the soluble nitrate of silver passes through as a 
filtrate, leaving the insoluble black cupric oxide on the 
filter paper. If the preparation of pure silver nitrate crys- 
tals is the object of the experiment, evaporate the filtrate 
to crystallization. If the desire is to recover the silver, 
this may be done by the addition of sodium chloride to the 
nitrate solution, as before, or by immersing a clean strip 
of copper in the solution, when the silver will be precipi- 
tated upon the copper. Silver obtained in this manner, 
however, is seldom entirely free from contamination with 
copper. 

EXPERIMENT No. 61.— The student should make a pure solution of 
silver nitrate, recrystallize a portion of it, and recover the silver from the 
remainder, as instructed above. 

PROPERTIES.— Silver is the whitest of metals, very 
brilliant, tenacious, malleable and ductile, in the last two 
qualities being inferior only to gold; if considered weight 
for weight, it is superior to gold, for while one grain of 
gold may be beaten so thin as to cover an area of 75 
square inches, a grain of silver may be made to cover 
98 square inches, though the foil of the former is much 
thinner than that of the latter. The extent of the mal- 
leability of gold and silver has never been absolutely 
determined, as the means employed have invariably 
failed before the property in either was exhausted. In 
tenacity silver is superior to gold. It is also harder than 
gold, but softer than copper, and is the best-known 
conductor of heat and electricity. It fuses at 1040° 
(1904°F.), far below the fusing point of either gold or 
copper. It volatilizes appreciably at full red heat; in 
the oxyhydrogen flame it boils, with the formation of a 
blue vapor. The fused metal readily absorbs oxygen 
gas (when fused under potassium nitrate it takes up as 
much as twenty times its volume). As the metal cools 



220 PRACTICAL DENTAI, METAUJJRGY. 

the oxygen escaping through the semi-solid crust on the 
surface of the fused mass produces very beautiful effects. 
Pure silver retains a trace of the absorbed oxygen per- 
manently. It is unaltered in the air at any temperature, 
but is readily acted upon by sulphur, phosphorus, or 
chlorine. 

EXPERIMENT No. 62.— Melt pure silver on a soldering block of 
asbestos or pumice-stone, and note the absorption of oxygen while molten, 
and the escape on cooling. 

COMPOUNDS WITH OXYGEN.— There are three 
oxides of silver, only one of which (Ag 2 0), however, can 
be regarded as a well-defined compound: 

The Monoxide, or Argentic Oxide, Ag 2 0, is a strong 
base, yielding salts isomorphous with those of the alkali- 
metals. It is obtained as a pale-brown precipitate on 
adding caustic potash to a solution of silver nitrate. 
Very soluble in ammonia, and slightly so in pure water, 
forming an alkaline solution. It is easily decomposed 
by heat; the sun's rays also effect a slight decomposition, 
as is the case in most compounds of silver. 

The other two oxides are the Argentous Oxide, Ag 4 0, 
and Silver Dioxide, Ag 2 2 . 

ACTION OF ACIDS ON SILVER.— Nitric Acid 
is the proper solvent for silver, and is most efficient 
when diluted about 50 per cent., but active whether con- 
centrated or dilute, with production of nitric oxide (N 2 O s ) 
and silver nitrate (AgN0 3 ). 

Sulphuric Acid, hot and concentrated, acts upon sil- 
ver, forming a sulphate which is sparingly soluble. 

Hydrochloric Acid, hot and concentrated, forms argen- 
tic chloride, slightly soluble in the concentrated reagent, 
but precipitated on dilution. 

Fused alkaline hydrates or nitre are without action 
upon silver; hence, it is used for the manufacture of 
crucibles for the fusion of caustic alkalis, etc. 



SIXVKR. 221 

ALLOYS. — Pure silver is too soft for coinage or com- 
mercial purposes; it is, therefore, alloyed variously for 
different purposes to increase its hardness. 

Gold. — Formerly silver was much used to alloy gold. 
The metals are easily mixed together, but do not appear 
to form definite compounds. With certain proportions 
of the metals the resulting alloys are more ductile, harder, 
more sonorous and elastic than either metal considered 
singly. 

Copper. — The alloys of copper and silver are more 
useful than any of the alloys of silver. In most coun- 
tries it forms the silver coins. In the United States the 
silver for coinage is alloyed with 10 per cent, copper, 
the proportion of each being stated in the thousandths; 
thus, pure silver being 1000 fine, the coin or "standard 
silver" is 900 fine, with 100 parts copper added. The 
German and French silver coins are of the same grade, 
those of Great Britain are 925 fine, with 75 parts of 
copper added, being known as "sterling" silver. Most 
silverware is of "sterling" fineness. The presence of 
copper does not modify the color of silver so long as 
the proportion of the former does not exceed 40 or 50 
per cent. Copper imparts to silver greater hardness, 
tenacity, and strength. 

Comparison of the silver dollar of the United States 
with that of Mexico: 

U. S. DOLLAR. MEXICAN DOLLAR. 

Pure Silver 371.25 grs. 377.14 grs. 

" Copper 41.25 " 40.65 " 

Total weight 412.50 " 417.79 " 

The Mexican dollar contains 5.89 grains more silver 
than the United States dollar, and .60 grains less copper. 
It is also 5.29 grains greater in weight than the United 
States dollar. 



222 PRACTICAL DENTAL METALLURGY. 

The Mexican dollar is equal to 0.866 of a Troy ounce. 

Zinc and silver have a great affinity for each other, 
and are consequently readily alloyed. 

Silver solder for soldering the metal is usually com- 
posed of an alloy with copper and zinc. The following 
are well adapted for the purpose. 

No. 1* No. 2.t 

Silver 66 parts. Silver 6 parts. 

Copper 30 ' * Copper 2 " 

Zinc 10 " Brass 1 " 

" When the material to be united is composed of pure 
silver and platinum, silver coin alloyed with, one-tenth 
zinc may be used as a solder." 

" Standard " is also an excellent solder for high fusing 
brass and German silver. If the article is to be soldered 
twice, this may be used first and the silver solder after- 
wards, x 

Dr. Kirk§ recommends the following compositions: 



ine Silver. 


Copper. 


Brass. 


Zinc 


4. 




3. 


. . . 


2. 




1. 


. . . 


19. 


1. 


10. 


5. 


66.7 


23.3 




10. 


50. 


33.4 


16.6 


. . . 


11. 




4. 


1. 



These may be used for soldering the surfaces of stand- 
ard silver. 

TESTS FOR SILVER IN SOLUTION.— Hydro- 
chloric acid and the soluble chlorides precipitate silver 
chloride, AgCl. It is a white, curdy substance, quite in- 
soluble in water, and nitric acid; one part of silver 

* Richardson, Mechanical Dentistry, p. 78. 

t Ibid. 

% Professor C. I,. Goddard. 

g Am. System of Dentistry, Vol. Ill, p. 879. 



SILVER. 223 

chloride is soluble in 200 parts of hydrochloric acid, 
when concentrated. When heated, it melts, and on 
cooling it becomes a grayish, crystalline mass, which 
cuts like horn. It is found native in this condition, con- 
stituting the mineral called horn silver. Silver chloride 
is decomposed by light, turning violet to brown (forming 
argentous chloride, Ag 2 Cl) both in the dry and in the 
wet state, very slowly if pure, and quickly if organic 
matter be present. It is reduced also when put in water 
with metallic zinc or iron. It dissolves very readily in 
ammonia and in a solution of potassium cyanide. This 
precipitation is the most delicate of the ordinary tests 
for silver, being recognized in solution in 250,000 parts 
of water. 

Potassium and sodium hydrate precipitate from 
solutions of silver salts, silver oxide, Ag 2 0, grayish 
brown, insoluble in excess of the reagents, easily soluble 
in nitric, acetic, or sulphuric acid, and in ammonia. 

Sulphuretted hydrogen throws down a black precipi- 
tate of silver sulphide, which is insoluble in potassium 
cyanide, dilute acids, or alkalis, but soluble in boiling 
nitric acid. 

Potassium chromate gives a red precipitate of silver 
chromate, Ag 2 Cr0 4 , which is soluble in ammonia, and 
concentrated nitric acid. 

EXPERI3IENT No. 63.— The student should perforin these tests. 

BLOW-PIPE ANALYSIS.— On charcoal, with 
sodium carbonate, silver is reduced from all its com- 
pounds in the blow-pipe flame, attested by a bright, 
malleable globule. Lead and zinc, and elements more 
volatile, may be separated from silver by their gradual 
vaporization under the blow-pipe. 



224 PRACTICAL DKNTAL METALLURGY. 

ELECTRO-DEPOSITION OF SILVER.— Silver is 
the most important and prominent metal in electro- 
plating processes. 

The solution generally used is the cyanide, and it may 
be prepared by either of two methods — the battery or the 
chemical process. 

The method of procedure in the former is simple, when 
thoroughly understood. First must be ascertained the 
percentage of actual cyanide in the salt used. If, say, it 
contains about 50 per cent., dissolve about one ounce in 
each quart of distilled water; or if it contains more, add 
less, and vice versa in proportion. Suspend a large anode 
and a small cathode of silver in the liquid, and pass a 
strong current of electricity through, until the required 
amount of metal is dissolved from the anode. As this 
process produces some caustic potash in the liquid, some 
of the strongest hydrocyanic acid may now be added to 
form cyanide, and more of the anode dissolved in the 
mixture by the battery. 

Making solutions for deposits by the chemical process 
is accomplished as follows: 

Take four parts of pure grain silver; and reduce it by 
mixing with nitric acid to argentum nitrate. Dissolve 
this in distilled water, in the proportion of one quart to 
every one-half ounce of silver used. At the same time 
make a solution of from two to three parts of cyanide of 
potassium in twenty or thirty parts of distilled water. 
This is to be added gradually to the solution of nitrate 
of silver as long as it produces a white precipitate. If 
too much be added, however, it will cause some of the 
precipitate to be redissolved and wasted. In such a 
case the liquid should be stirred and then allowed to 
settle clear. A small amount of nitrate of silver dis- 
solved in distilled water should be added as long as it 



SILVER. 225 

produces a white cloud. This may be better conducted 
by using a glass vessel and observing the precipitate as it 
dissolves. The liquid should now be left to settle until 
quite clear, and the clear portion then decanted, and the 
precipitate washed four or five times in a large quantity 
of water by simply adding the water, stirring, and 
allowing it to settle again and decanting as before. 
Next dissolve from six to eight parts of cyanide of potas- 
sium in twenty parts of distilled water, adding it a 
portion at a time, with free stirring, to the wet cyanide 
of silver, until the whole is barely dissolved; then add 
about three parts more of cyanide of potassium to form 
free cyanide, and sufficient distilled water to reduce the 
whole to the proportion of about one-quarter of an 
ounce of silver to the quart; finally, when all the free 
cyanide is dissolved, filter the solution and it is ready 
for use. The specific gravity of the solution should be 
maintained at between 1.8 and 1.15. 

Deposit solutions are very numerous, but, in the 
author's judgment, the above is best adapted for a good, 
reguline solid deposit. 

Knowledge of the management of solutions is essential. 
There are varying circumstances which must be noted 
in order to keep them in good condition for a reguline 
deposit. New solutions do not work as well, usually, as 
old ones, provided the latter is not too old. Solutions of 
two or three years of age work probably the best. They 
change from many causes; they become dirty and con- 
centrated from exposure; increase or decrease in their 
relative proportions of cyanide and metal; they acquire 
other metals in solution, dissolved from the anode and 
corroded from the cathode; plaster and plumbago accu- 
mulate in them, and in consequence of which they should 
be filtered; they gradually decompose, become brown, 



226 PRACTICAL DENTAL METALLURGY. 

discolored, and evolve ammonia by exposure to light, 
especially if they contain too much free cyanide; therefore, 
all these deviations from the proper condition should be 
corrected. The specific gravity should be maintained, 
and the proper amount of metal and cyanide kept in solu- 
tion. To determine any disproportion in the latter, place 
25 grams of the solution in a test-tube of proper size and 
add to it, at first freely, and afterwards gradually, until 
at last, drop by drop, with constant stirring, a solution of 
one gram of crystallized nitrate of silver in ten grams of 
distilled water. If the precipitate formed is dissolved 
rapidly, with but little need of stirring, there is too much 
cyanide. If, however, it does not dissolve, even after 
much stirring, there is too little cyanide; but if it who'ly 
dissolves (the latter part quite slowly) the proportion of 
silver to cyanide is about correct. 

Many other minor troubles not mentioned are encoun- 
tered, which must be corrected by means gathered only 
from experience in working the process. 

The process for making dental bases by electro-depo- 
sition on the plaster cast of the mouth was patented 
February 5, 1889, by Joseph G. Ward of Irvington, N. J. 

The author has had some experience in the work; in 
fact, was engaged in perfecting a process for the same 
result when Mr. Ward secured his patent. The method 
of proceeding in the preparation of a dental base is as 
follows: 

A true impression of the mouth is secured, and from 
this a cast is obtained by filling in the usual manner. 
After the cast has become thoroughly dry it should be 
soaked in hot fluid paraffin, until saturated, and before 
cooling the surface wiped clean of all superflous ad- 
hesions which might in any way destroy the exactness 
of the model. The cast is then coated freely where the 



SILVER. 227 

deposit is desired with a mixture of equal parts of pure 
finely pulverized plumbago and the finest tin-bronze 
powder or any other conducting substance suitable under 
the circumstance. This recommended is applied with a 
thick, short-haired camel's-hair pencil. The cast is now 
so wired that perfect connection is made with the pala- 
tine, buccal, and labial surfaces. From these guiding 
wires a cathode-hook suspends the cast in the solution. 
After the metal has been deposited to a sufficient thick- 
ness, the cast, with its deposit, is to be taken from the 
bath, the deposit removed from the cast, trimmed and 
polished; but if it is desired to have the plate of increased 
thickness at any part to give the appearance of a turned- 
rim, etc., the cast, with the deposit adhering to it, may 
be removed from the bath, and all the exposed surface of 
the deposit, except the portions to be thickened, may be 
covered with a coating of wax or some other non-con- 
ducting substance, and re-submerged in the bath and left 
there until the required thickness of deposit is secured in 
the parts desired. It may then be taken from the bath, 
burnished, trimmed by scraping, burring and filing to the 
proper shape and thickness, then polished, and spurred. 
A thick plating of gold should now be added to the 
properly shaped plate, or the rubber for the attachment 
of the teeth will not harden and adhere to the plate dur- 
ing the process of vulcanization (the sulphur of the 
vulcanite combining with the silver). After the teeth 
have been attached and the vulcanite and all properly 
finished, a second coating of gold should be electro-plated 
over it all to cover portions that had been made bare in 
finishing the vulcanite. 

The denture may be made by depositing the metal 
directly on the teeth as in cheoplastic work, and, where 



228 PRACTICAL DENTAL METALLURGY. 

necessary, clasps may be formed. Broken dentures have 
been soldered with 18-carat gold solder. 

Crowns and bridge-work may also be made in various 
ways by this process. 

EXPERIMENT No. 64.— The process should be demonstrated in the 
metallurgical laboratory by the instructor. 



CHAPTER XVII. 

IRIDIUM. 

Iridium. Symbol, Ir. 

Valence, II, IV. Specific gravity, 22.40. 

Atomic weight, 192. G5. Malleable, at red heat. 

Melting point, oxhydrogen Chief ore, Iridosmine. 

flame. Crystals, hexagonal. 
Color, steel-white. 

OCCURRENCE.— This metal occurs chiefly as a 
native alloy of iridium and osmium, known as osmiridium 
or iridosmine. It is also found thus combined with plat- 
inum, and is contained in gold from several localities, 
especially that from some mines of California and in the 
Frazer River district of British Columbia, causing much 
inconvenience. It is observed in hexagonal crystals, 
rarely in hexagonal prisms, commonly in irregular flat- 
tened grains, of a tin-white color, in the residues after 
the extraction of platinum from its ores. 

REDUCTION.— It is obtained from its native alloy 
by mixing with an equal weight of dry sodium chloride, 
and heating to redness in a glass tube, through which a 
moist stream of chlorine gas is transmitted. The mixture 
of iridium and osmium sodio-chlorides thus formed is 
dissolved in water and evaporated, and distilled with 
nitric acid, removing the osmium as osmic acid; when its 
complete removal is thus effected, ammonium chloride is 
added to the residual solution, which precipitates the 
ammonio-chloride of iridium as a dark red-brown pre- 
cipitate. From this, spongy metallic iridium is obtained 
in the same manner as the production of spongy platinum. 

PROPERTIES.— Iridium is a steel-white metal, 
exceedingly hard, brittle when cold, but somewhat 
malleable when at red heat, having a specific gravity of 



230 PRACTICAL DENTAL METALLURGY. 

22.40, unaltered in air, and fusible only in the oxyhydro- 
gen flame. If the precipitated metal be moistened with a 
small quantity of water, pressed tightly between filter- 
paper, and then very forcibly in a press, and calcined at 
a white heat, it may be obtained in the form of a very 
hard compact mass, capable of taking a good polish, but 
still very porous, and having a specific gravity not to 
exceed 16. 

COMPOUNDS WITH OXYGEN.— Iridium forms 
three oxides: 

The Monoxide, or Hypoiridious Oxide, IrO, is but 
little known, and upon being exposed to the air is 
quickly converted into a higher oxide. 

The Sesquioxide, or Iridious Oxide, Ir 2 O s , may be 
formed by exposing the metal at a red heat to the action 
of the oxygen of the air. It is a black powder, insoluble 
in the acids and much used for imparting an intense black 
to porcelain. 

The Dioxide, or Iridic Oxide \ Ir0 2 , is also a black 
powder, obtained by heating the tetrahydroxide in a 
current of C0 2 . It is insoluble in acids, and is said to 
be the most stable oxide of the metal. 

ACTION OF ACIDS ON IRIDIUM.— The pure 
metal itself is not acted upon by the acids, but when 
reduced by hydrogen at a low temperature, it oxidizes 
slowly at a red heat; and may be dissolved in nitro- 
hydrochloric acid. It is, however, usually rendered 
soluble by fusing it with potassium nitrate and caustic 
potash. Its hydroxides are also soluble. It forms two 
chlorides, IrCl 3 and IrCl 4 and analogous iodides, and 
three sulphides analogous to the three oxides. 

ALLOYS.— With Mercury. Dr. Kirk relates that 
"Bottger formed an amalgam with iridium by immers- 
ing sodium amalgam in an aqueous solution of chloriri- 



IRIDIUM. 231 



date of sodium; he describes the amalgam as soft and 
viscid." 

With Gold iridium forms a malleable and ductile alloy, 
its color depending upon the proportions of the metals. 

Platinum and iridium form some very valuable and 
useful alloys.* Aside from these, and the use of the 
metal and its alloy with phosphorus for pointing gold 
pens, iridium is of little value. 

With Silver it is claimed there is no alloy; and that 
after exposing a mixture of these metals to a high tem- 
perature, or attempting to pour out the contents of the 
crucible, silver alone flows out and a thick mass is left 
in the crucible. 

Phosphor-iridium — f"For preparing larger pieces of 
iridium than found in nature, for making points for the 
Mackinnon stylographic pen, Mr. John Holland of Cin- 
cinnati has devised the following ingenious process; 
The ore is heated in a Hessian crucible to a white heat, 
and, after adding phosphorus the heating is continued 
for a few minutes. In this matter a perfect fusion of 
the metal is obtained, which can be poured out and cast 
into any desired shape. The material is about as hard 
as the natural grains of iridium, and, in fact, seems to 
have all the properties of the metal itself. 

"Phosphor-iridium, as this metal may be called, pos- 
sesses some very remarkable properties. It is as hard, if 
not harder, than iridosmine, from which it is prepared. 
It is somewhat lighter, owing to its percentage of phos- 
phorus and increase of volume. It is homogeneous and 
easy to polish, and forms some alloys impossible to pre- 
pare in any other manner. It combines with small 
quantities of silver, and forms with it the most flexible 
and resisting alloy of silver. With gold or tin no alloy 
has thus far been obtained. Added in small quantities 
to copper, it furnishes a metal possessing very small re- 
sistance to friction, and is especially adapted for articles 

* See chapter on Platinum. 

f Metallic Alloys, Brannt, p. 347. 



232 PRACTICAL DENTAL METALLURGY. 

subjected to great pressure. This alloy seems to possess 
more than any other metal the power of retaining lubri- 
cants. With iron, nickel, cobalt, and platinum, phos- 
phor-iridium forms combinations in all proportions, 
which are of great importance. With iron an alio}' is 
obtained which retains the properties of phosphor- 
iridium, although its hardness decreases with a larger 
addition of iron. The alloy is slightly magnetic, and is 
not attacked by acids and alkalis, and the best file pro- 
duces no effect upon it, even if it contains as much as 50 
per cent, of iron. With more than 50 per cent, of iron, 
the power of resistance decreases gradually, and the 
nature of the metal approaches that of iron." 



CHAPTER XVIII. 

PALLADIUM. 

Palladium. Symbol, Pd. 

Valence, II, IV. Specific gravity, 11.4. 

Atomic weight, 105.73. Malleability, 11th rank. 
Melting point, 1600° (2912° P.). 

Ductility, 10th rank. Chief ore. In gold and platinum. 

Conductivity (heat), — Conductivity (electricity), 18.4. 

(Silver being 100.) 

Specific heat, 0.0593. Crystals, fibrous. 
Color, platinum-white. 

OCCURRENCE.— Palladium is found native in com- 
pany with platinum from which it is distinguishable by- 
its fibrous structure. It is usually found, however, 
alloyed with platinum and with some specimens of 
Brazilian gold. 

REDUCTION.— When the solution of crude platinum 
from which the greater part of the metal has been pre- 
cipitated by sal-ammoniac, is neutralized by sodium 
carbonate, and mixed with a solution of mercuric cya- 
nide, palladium cyanide separates as a whitish insoluble 
substance, which on being washed, dried, and heated to 
redness, yields metallic palladium in a spongy state. 
The palladium may then be welded into a mass in the 
same manner as platinum.* 

PROPERTIES.— Palladium is a white metal, much 
resembling platinum, though somewhat darker in color. 
Its specific gravity differs greatly from that of platinum, 
being only 11.4. It is also very much less ductile and 
malleable than that metal; it is the most fusible of the 
platinum group, yet it barely melts at the highest 
wind-furnace heat, or about the temperature at which 

* Manual of Chemistry, Physical and Inorganic. Watts. 



234 PRACTICAL DENTAL METALLURGY. 

malleable iron fuses, 1600° C, and when heated to redness 
and exposed to the air, especially in its spongy state, it 
acquires a blue or purple superficial film of oxide, but 
may be restored to its brightness and luster upon being 
heated to a more intense degree, the oxide being reduced. 
If heated and fused in air it is apt to vegetate on cooling, 
similarly to silver. 

The metal is most remarkable for its property of " oc- 
cluding" or absorbing hydrogen. According to Graham 
the compact metal when immersed in cold hydrogen gas 
takes up little or none of it; but at higher temperatures 
very considerable occlusions take place. A certain 
specimen of palladium-foil at 245° C. was found to absorb 
526 times its own volume of hydrogen; and at between 
90° and 97° C. , 643 times its volume. The hydrogen, as 
in the case of platinum, is retained in the metal on cool- 
ing. Graham views hydrogenized palladium as a true 
alloy, containing its hydrogen in the form of a metal — 
" hydrogenium." Palladium has not the power of ab- 
sorbing oxygen or nitrogen. If palladium be used as 
the negative electrode in the electrolysis of water, the 
coefficient of absorption is very high; especially is this 
the case when the palladium was produced electrolyti- 
cally and hydrogenized while itself in the nascent state. 
Such metal cold was found to contain 982 volumes of 
hydrogen, corresponding approximately to the formula 
Pd 4 H 3 . The element does not lose any of its metallic 
properties by being hydrogenized, but it loses nearly 10 
per cent, of its specific gravity. At the same time its 
bulk is increased about one-tenth. 

DENTAL APPLICATIONS.— Formerly palladium 
was used to some extent as a base for artificial dentures. 
Its lightness (having little more than half the specific 
gravity of gold), hardness, and resistance to discoloring 



PALLADIUM. 235 



and corroding influences made it desirable; but then it 
might be had for % its present price — which practically 
excludes it from the dental laboratory to-day. 

COMPOUNDS WITH OXYGEN. — Palladious 
Oxide, the Monoxide, PdO, may be prepared by evapo- 
rating to dryness, and cautiously heating the solution of 
palladium in nitric acid. It is of black color, but slightly 
soluble in acids, and decomposed by high temperature. 

Palladic Oxide, the Dioxide, Pd0 2 , is not known in the 
separate state. From palladic chloride solutions alkalis 
and their carbonates throw down a brown precipitate, 
hydrated palladic oxide combined with the alkali. The 
hydroxide is decomposed by high heat; dissolves slowly 
in acids, forming yellow solutions. 

ACTION OF ACIDS ON PALLADIUM.— In 
Hydrochloric or Sulphuric Acid boiling and concen- 
trated palladium is slightly soluble, forming palladious 
chloride, PdCl 2 and palladious sulphate, PdS0 4 . 

Nitric acid dissolves it slowly, but it is more readily 
soluble in a mixture of nitric and nitrous acids, forming 
palladic nitrate, Pd (N0 3 ) 4 . 

Nitro-hydrochloric acid is a ready solvent for this 
metal, forming palladic chloride, PdCl 4 . The solution is 
a deep brown color, decomposed upon evaporation with 
a liberation of chlorine and becoming PdCl 2 . 

ALLOYS. — With Mercury, in the finely divided state, 
it readily combines to form a gray plastic amalgam. 
This union is attended with the evolution of some heat, 
and is said to result in a definite chemical compound. 
(See chapter on Amalgams.) 

Palladium renders its alloys harder and more brittle. 
These are chiefly used in the manufacture of fine 
watches, and the most important are those with silver and 
the so-called palladium bearing-metal. 



236 PRACTICAL DENTAL METALLURGY. 

Gold and palladium combine to form a hard alloy less 
malleable and ductile than gold in proportion to the 
amount of palladium it contains. 

Silver. — An alloy of palladium 9 parts and silver 1 
part was used for dental bases, as was also the following: 
platinum 10, palladium 8, and gold 6 parts. Mr. Fletcher 
says * * * a silver alloy poor in palladium is worthless, 
as a large amount of the latter is necessary to protect it 
from sulphuretted hydrogen. And, further, that pure 
palladium is the best metal known for plates for artificial 
teeth, owing to its high specific heat, its extreme light- 
ness and hardness, requiring no alloy, and also to its 
absolute freedom from tarnish. 

The same author further says: " As an alloy, the pres- 
ence of palladium in small quantities is frequently objec- 
tionable, * * * almost inadmissible, even in so small a 
proportion as 1 to 2000 in silver for making amalgams." 

With nickel it forms a malleable alloy susceptible to 
high polish. 

With antimony, bismuth, tin, zinc, iron, and lead 
it combines to form very brittle alloys. 

Palladium bearing-metal. — An uncommonly hard 
alloy used as bearings for fine watches, and is said to 
produce less friction upon arbors of hard steel than the 
jewels generally used. The composition is, palladium 24, 
gold 72, silver 44, and copper 92. 

TESTS FOR PALLADIUM IN SOLUTION.— Salts 
of palladium may be discriminated by: — 

Sulphuretted hydrogen or ammonium hydro-sul- 
phide, which throws down a black precipitate of palladious 
sulphide, insoluble in alkaline sulphides, but soluble in 
hydrochloric acid. 

Potassium iodide gives a black precipitate of palla- 
dium iodide from palladious chloride. 



PALLADIUM. 237 



Potassa or soda yields a red precipitate soluble in 
excess of alkali if heated. 

Mercuric cyanide, the characteristic test, gives a yel- 
lowish-white gelatinous precipitate of palladious cyanide 
from solutions of palladious chloride, which is soluble in 
hydrochloric acid. 

Nearly all the compounds of palladium are reduced by 
heat, before the blow-pipe^ to a "sponge." If this be 
held in the inner flame of an alcoholic lamp it absorbs 
carbon at a heat below redness; if then removed from the 
flame it glows vividly in the air, till the carbon is all 
burnt away — (distinction from platinum). 

ELECTRO-DEPOSITION OF PALLADIUM.— 
The metal may be deposited from a cyanide of potassium 
solution by the battery process, yielding thick metallic 
deposits in a white reguline state. 



CHAPTER XIX. 
PLATINUM. 

Platinum. Symbol, Pt. 

Valence, II, IV. Specific gravity, 21.46. 

Atomic weight, 194.41. Malleability, 6th rank. 
Melting point, oxyhydrogen 

name, 1770° C. 

Ductility, 3d rank. Tenacity, 3d rank. 

Conductivity (heat), 8.4. Conductivity (electricity), 18.8. 

(Silver being 100.) 

Specific heat, 0.0322. Chief ore, Polyxene. 

Color, bluish silver-white. Crystals, octahedral. 

OCCURRENCE.— The ore of platinum, "polyxene," 
which is a most complex mixture of a number of heavy 
reguline species of platinum, osmiridium, iron-platinum, 
platin-iridium, iridium, palladium, gold, and a number 
of non-metallic species, notably chrome-iron ore, mag- 
netic iron oxide, zircone, corundum, and occasionally 
also diamond, is found in the province of Choco, South 
America, where it was first discovered in 1736, in New 
Granada, Barbacos, California, and Australia, but chiefly 
in alluvial deposits in the Ural district. The vari- 
able percentages of the several components range ap- 
proximately as follows: Platinum, 60 to 87; other 
polyxene metals, 3 to 7; gold, 2 and more; iron, 4 
to 12; copper, to 4; non-metallic gangue, 1 to 3. Gold 
is separated by amalgamation when it exists in any con- 
siderable quantities. 

Platinum is rarely found in large nuggets, but usually 
in granules, which are generally small, but occasionally 
assume considerable dimensions. The Demidoff Museum 
contains a native platinum lump weighing 21 pounds 
troy. 



PLATINUM. 239 



REDUCTION.— The extraction of platinum is accom- 
plished by two distinct methods. The first, devised by 
Wollaston, which produces the purest metal, is more of 
a chemical than a metallurgical process, a modification 
of the method by Herseus is as follows: The ore is 
digested within glass retorts in dilute aqua regia, by 
which the platinum, palladium, part of the iridium, and 
more or less of the other metals pass into solution, the 
platinum, palladium, and iridium as tetrachlorides. The 
solution is then evaporated to dryness, and the residue 
heated to 125° C, to reduce the palladic and iridic chlor- 
ides to the lower stages of PdCl 2 and Ir 2 Cl 6 , which 
form soluble double salts with sal-ammoniac. The heated 
residue is dissolved in water acidulated with hydrochloric 
acid; the solution filtered, and mixed with a hot con- 
centrated solution of sal-ammoniac, when a quite pure 
chloroplatinate, PtCl 6 (H 4 N) 2 , comes down in a yellow 
precipitate, which is washed first with a saturated sal- 
ammoniac solution, then with hydrochloric acid. This 
precipitate needs only to be exposed to a dull red heat to 
be converted into "spongy platinum," i. e., metallic 
platinum in the form of a gray, porous mass. 

The second method, known as Deville's, is based upon 
the tendency of platinum to be dissolved in melted lead. 
The ore is fused with an equal weight of galena (sulphide 
of lead) and as much of the oxide of lead. The sulphur 
and oxygen escape as sulphur dioxide, the reduced lead 
dissolving the platinum, and leaving the very heavy 
alloy of osmium and iridium to sink to the bottom un- 
dissolved. The upper portion containing the platinum 
is then ladled out (see chapter on Silver) and cupelled, 
when the latter metal is left in a spongy mass, the lead 
having passed off as the oxide. 



240 



PRACTICAL DENTAL METALLURGY 



FUSING PLATINUM.— By means of the oxydrogen 
blow-pipe the spongy platinum is easily reduced to a 
compact mass, where formerly it was only obtained so, 
relatively, by the very tedious and laborious means of 
welding. 

The furnace for fusing platinum (Fig. 34) is at once a 
cupel and furnace, consisting of two thoroughly burned 
lime blocks with a basin-like concavit3 r in each, and fitted 




one over the other. The concavity in the lower block 
forms the bed of the furnace, and is provided with a gut- 
ter leading from the basin to the outside. Through the 
top is passed the oxyhydrogen blow-pipes. They each 
consist of two concentric tubes, or a smaller within a 
larger. Through the outer, or larger, tube the hydrogen 
or illuminating gas is passed, and through the inner, or 



PLATINUM. 241 



smaller, the oxygen is forced into the center of the flame. 
The tubes are of copper, tipped with platinum. 

Platinum scraps are melted by first heating up the 
furnace and then introducing them through an opening 
in the side. In the case of platinum sponge the mass is 
introduced before heating up the furnace, and it is here 
that the furnace acts as a cupel; the impurities remaining 
in the metal are oxidized and volatilized or absorbed by 
the lime of the furnace. The temperature produced is 
supposed to be about 2870° C. Osmium does not melt at 
this point, but it, with palladium and gold, is volatilized, 
if present. 

Platinum may also be fused by placing the metal 
between the carbon tips of an arc light. 

EXPERIMENT No. 65. — Fuse platinum under flame of oxyhydrogen 
(or oxygen and illuminating gas) blow-pipe. 

EXPERIMENT No. 66.— Fuse platinum by means of the electric cur- 
rent. 

EXPERIMENT No. 67.— Tin a piece of platinum by dipping it into 
molten tin. Observe that the tinned platinum -will melt over the Bunsen 
flame like wax. When platinum is added to dental-amalgam alloys containing 
tin there need be no fear that it will not be melted. 

PROPERTIES.— The metal is bluish silver-white, 
about as soft as pure copper, and has a specific gravity 
of 21.46. It is tough, ductile, and malleable, and may 
be rolled or beaten into foil or drawn into wire of almost 
microscopic fineness. Dr. Arendt states* that a cylinder 
of platinum, one inch in diameter and five inches long, 
may be drawn into a wire sufficiently long to encircle the 
earth at the equator. The fine wire used in the microm- 
eter eye-piece of microscopes suggested by Wollaston is 
made by drawing a composite wire of platinum coated 
with silver to its greatest attenuation, and then dissolv- 

*Dr. Kirk in American System of Dentistry, Vol. Ill, p. 887, from Anorgan- 
ischen Chemie. 



242 PRACTICAL DENTAL METALLURGY. 

ing off the silver in nitric acid. Platirmm possesses 
tenacity in a high degree, being just inferior to iron and 
copper. The fusing point, according to Violle, is 1779° C. 
When heated much above its fusing point, it soon begins 
to volatilize. The fused metal, like silver, absorbs oxy- 
gen, and consequently "spits" on freezing. At a red 
heat it "occludes" hydrogen gas. The volume of hy- 
drogen absorbed by unit volume of metal at a red heat, 
under one atmosphere's pressure, was found, in the case 
of the fused metal, to vary from 0.13 to 0.21, volume 
measured cold; in the case of merely welded metal from 
2.34 to 3.8 volumes. Oxygen, though absorbed by the 
liquid, is not occluded by the solid metal at any tempera- 
ture, but when brought in contact with it at moderate 
temperatures, suffers considerable condensation at its sur- 
face, and in such a state exhibits a high degree of chem- 
ical affinity. When a jet of hydrogen gas strikes a layer 
of spongy platinum it causes it to glow and take fire. 

The most striking effect of the metal for absorbing gases 
is demonstrated in the finely divided state known as 
"platinum black." This state is produced by dropping 
platinum chloride solution into a boiling mixture of 
3 parts of glycerine and 2 of caustic potash. Platinum 
black is said to absorb 800 times its volume of oxygen 
from the air, and is, therefore, a most active oxidizing 
agent, acting catalytically, i. e., after having given up its 
oxygen to the oxidizable substance it takes up a fresh 
supply from the atmosphere. 

DENTAL APPLICATIONS.— Platinum was intro- 
duced in France as early as 1820 for a base in con- 
tinuous-gum work. Its low rate of expansibility under 
increased temperature, its coefficient being about equal 
to that of glass, and its very high fusing point make it 
most useful for continuous-gum work, and for pins for 



PLATINUM. 243 



artificial teeth. Its comparatively great resistance to 
chemical agents insures it against corrosive action, and 
places it on an equality with gold for dental bases, crowns, 
and bridge-work. 

Platinum and gold is used as a filling material in the 
form of platinum and gold folds, platinized gold folds, 
and platinum and gold foil. The color of this material 
inserted as a filling is not as beautiful as that of either 
gold or platinum alone. The yellow of gold having 
almost entirely disappeared leaves an ashen effect to the 
platinum, which very much detracts from its character- 
istic color and appearance. The advantage it possesses 
over gold is its tough, resistant property — making a sur- 
face that will stand the abrasive action of mastication 
much better than gold. 

Coils of platinum are useful in dental offices in various 
forms of electric heating devices. The heat is free from 
products of combustion and can be most accurately con- 
trolled. A device of this nature is especially valuable in 
annealing gold. 

COMPOUNDS WITH OXYGEN.— Platinum forms 
two compounds with oxygen. 

Platinous Oxide, or Monoxide, PtO, is obtained by 
digesting the platinous chloride with caustic potash as a 
black powder, soluble in excess of the alkali. It is not 
known in the separate state; is a feeble base, and decom- 
posed by heat, leaving metallic platinum. 

Platinic Oxide, or Dioxide, Pt0 2 , also a weak base, 
occasionally acting as an acid; hence, it is sometimes 
termed platinic acid. It is best prepared by adding 
barium nitrate to a solution of platinic sulphate; 
barium sulphate and platinic nitrate are thus formed, 
and from the latter caustic soda precipitates one-half of 
the platinum as platinic hydroxide. The hydroxide is 



244 PRACTICAL DENTAL METALLURGY. 

a bulky brown powder, which, when gently heated, 
becomes black and anhydrous. If this oxide be dissolved 
in dilute sulphuric acid and the solution mixed with 
excess of ammonia, a black precipitate of fulminating 
(explosive) platinum is obtained, which detonates vio- 
lently at about 400° F. 

ACTION OF ACIDS ON PLATINUM.— The 
metal is not sensibly tarnished by sulphuretted hydrogen 
vapor or solution; and is not attacked at any tempera- 
ture by nitric, hydrochloric or sulphuric acid; but it 
dissolves in nitro-hydrochloric acid to form platinic 
chloride. It is, however, less readily soluble in this acid 
than gold. 

ALLOYS. — Platinum alloys with most of the metals. 

With mercury spongy platinum unites to form an ex- 
ceedingly unctious amalgam. It does not unite readily, 
and its union is best accomplished by continuous rubbing 
in a warm mortar. 

Iridium from 10 to 15 per cent, added to platinum 
greatly increases its hardness, elasticity, infusibility, and 
resistance to chemical action. Platinum alloyed with 
iridium can be made very useful in dentistry to strengthen 
weak parts of partial continuous-gum and partial vul- 
canite dentures. An alloy of 78.7 platinum and 21.3 
iridium will withstand the action of aqua regia. Equal 
parts of the metals form a very brittle alloy. 

Gold and platinum form an alloy of great value for the 
construction of dental bases. Platinum gives to gold a 
greater hardness and elasticity. Two parts to one of 
gold forms a brittle alloy, while with equal parts the 
alloy is malleable. Prinsep found that 7 parts of gold 
and 3 parts of platinum. formed an alloy infusible in the 
strongest blast-furnace. Gold 11 parts and platinum 1 
part form a grayish-white alloy, having somewhat the 
appearance of tarnished silver. 



PLATINUM. 245 



Silver. — By small additions of platinum to silver its 
pure white color is changed to a gray, and its hardness 
is increased. The alloys are difficult to make, on account 
of the separation of the platinum, owing to its greater 
specific gravity. 

Platine au titre, an alloy composed of from 65 to 83 
per cent, of silver, has been used for dental bases in pref- 
erence to coin silver, on account of its resistance to 
chemical action and its greater elasticity. Nitric acid 
will dissolve an alloy of silver and platinum when the 
latter is not present, to exceed 10 per cent. 

Cadmium and platinum unite, to form a definite 
compound, having the formula of PtCd 2 . 

Copper and platinum, equal parts, form a gold-col- 
ored alloy tarnishing in air. 

Lead and tin unite in all proportions with platinum. 
Those of tin are hard and brittle, with comparatively 
low fusing points. Those of lead are harder, whiter and 
tougher than pure lead. 

TESTS FOR PLATINUM IN SOLUTION.— Sul- 
phuretted hydrogen throws down, after heating, a 
blackish-brown precipitate. 

Potassium or ammonium hydrate each throws down 
a very characteristic yellow crystalline precipitate, 
the former soluble in large excess of precipitant, and the 
latter, when dried and heated, yielding metallic platinum. 

By the reducing blow-pipe flame, the compounds of 
platinum are reduced to spongy platinum. 

ELECTRO-DEPOSITION OF PLATINUM.— Good, 
thick, reguline deposits of platinum may be obtained 
from a cyanide solution made by dissolving the chloride 
in a solution of potassium cyanide. The anode is not 
dissolved; therefore, the salt must be replaced. 

Zinc and iron precipitate the metal in a finely divided 
state. 



CHAPTER XX. 
GOLD. 

Aurum. Symbol, Au. 

Valence, I, III. Specific gravity, 19.265. 

Atomic weight, 196.15. Malleability, 1st rank. 

Melting point, 1100° (2012° F.). Tenacity, 5th rank. 

Ductility, 1st rank. Chief ore — found native. 

Conductivity (heat), 53.20. Conductivity (electricity), 77.96. 

(Silver being 100.) 

Specific heat, 0.0324. Crystals, octahedral. 
Color, yellow. 

OCCURRENCE.— Gold is found in nature chiefly in 
the metallic state, or as native gold, and. less frequently 
in combination with tellurium, lead, and silver. It is 
also found combined, or, perhaps, more strictly speak- 
ing, minutely mixed with pyrites and other sulphides, 
more commonly called " sulphurettes. " 

Native gold occurs rather frequently in crystals be- 
longing to the cubic system, the octahedron being the 
commonest form, but other and complex combinations 
have been observed. Large crystals are rarely well de- 
fined, owing to the softness of the metal, the points 
being commonly rounded. The most characteristic forms, 
however, are the nuggets or pepites. These, when of a 
weight less than one-quarter to one-half an ounce, are 
kno wn as gold dust. 

Kxcept the larger nuggets, which are usually more or 
less angular or irregular, gold is generally found in a 
bean-shaped or somewhat flattened form, the smallest 
particles being scales of scarcely appreciable thickness, 
and owing to their small bulk, as compared with their 
surface, they are frequently suspended in water and may 
be washed away by a rapid current; hence, they are 
known afloat gold. 



GOLD. 



247 



In the museum of the Mining Bureau in San Fran- 
cisco are several plaster of Paris models of famous gold 
nuggets found in the various gold regions of the world. 
The largest single piece of gold ever found was taken 
out at Ballarat, Victoria, Australia. It weighed 2166 
troy ounces, and was valued at $41,882. The second 
largest was discovered in the Ural Mountains district, 
and weighed 1200 ounces. The third largest, which was 
also found in Victoria, Australia, weighed 1121 ounces, 
and was valued at $22,000. 

The physical properties of native gold are quite similar 
to those of the melted metal and its alloys. The com- 
position varies considerably in different localities as shown 
in the following table: 

ANALYSIS OF NATIVE GOLD FROM VARIOUS LOCALITIES. 



Locality. 


Gold. 


Silver. 


Iron. 


Copper. 


EUROPE: 

British Isles — 

Vigra and Clogau 

Wicklow (River) 

Transylvania 

ASIA: 

Russian Empire — 

Brezovsk 


90.16 
92.32 
60.49 

91.88 
98.96 

90.05 

94.00 
88.05 
76.41 
90.12 
81.00 
84.25 

87.78 
99.25 


9.26 

6.17 

38.74 

8.03 
0.16 

9.94 

5.85 
11.96 
23.12 

9.01 
18.70 
14.90 

6.07 
0.65 


Trace 

.78 

Trace 
.05 


Trace 
0.77 

.09 


Ekaterinburg 


.35 


AFRICA: 

Ashantee 




AMERICA: 

Brazil 






Central America 






Titiribi 




0.87 


California 




Mariposa 

Cariboo 






6.15 


.03 


AUSTRALIA: 

South Australia 




Ballarat 











248 PRACTICAL DENTAL METALLURGY. 

The most important minerals containing gold are: 

Sylvanite, or graphic tellurium, (AgAu)Te 2 , con- 
taining 24 to 2 6 per cent: 

Calaverite, AuTe 2 , containing 42 per cent.; 

Nagyagite, or foliate tellurium, of a complex and 
rather indefinite composition, and containing from 5 to 9 
per cent, only of gold. 

The calaverite, a nearly pure telluride of gold, has 
been found to some considerable extent in Calaveras 
County, California. 

The minerals of the second class, called auriferous, are 
comparatively numerous, and include many of the metal- 
lic sulphides. The most important of these are iron 
pyrites and galena; the first of these is of great practical 
importance, being found in many districts exceedingly 
rich, and, next to the native metal, is the most prolific 
source of gold. 

A Native Amalgam of gold is found in California, 
but rarely in any considerable quantities. 

Gold is so widely distributed throughout the earth's 
crust that few regions may be said to be destitute of 
slight traces of it; yet it has been found in comparatively 
few localities in quantities sufficient for economical ex- 
traction. The principal supplies of the metal have been 
derived from Africa, California, Australia, Mexico, Bra- 
zil, Ural Mountains, Transylvania, etc. 

California was for many years chiefly known to the 
world as the region where gold was found in extraordi- 
narily large quantities. Great excitement was occa- 
sioned by the discovery of the precious metal in Januar)?-, 
1848, and its subsequent extraction from the placers of 
the Sierra Nevada Mountains. The gold regions of Cali- 
fornia are the mountain counties lying between Shasta 
and lessen on the north, and Fresno on the south. At 



GOLD. 249 

the time of their greatest productiveness the yield reached 
about $65,000,000 in value a year; this was from 1850 
to 1853. 

The association and distribution of gold may be 
considered under two different heads ; namely, as it 
occurs in mineral veins, and in alluvial or other super- 
ficial deposits which are derived from the waste or disin- 
tegration of the former. As regards the first, it is 
usually found in quartz veins or reefs traversing slaty or 
* crystalline rocks, either alone or associated with such 
metals as iron, copper, tellurium, and rarely bismuth, or 
such minerals as magnetic and arsenical pyrites, galena, 
specular iron ore, and silver ore, and rarely with the 
sulphides of molybdenum, tungstate of calcium, bismuth, 
and tellurium minerals. 

In the second or alluvial class (placers) of deposits it 
is associated chiefly with those minerals of great density 
and hardness, such as platinum, osmiridum, and other 
metals of the platinum group, tinstone, chromic, mag- 
netic, and brown iron ores, diamond, sapphire, ruby, 
topaz, etc., which represent the more durable original 
constituents of the rocks whose disintegration has 
furnished the detritus. 

MINING AND EXTRACTION.— The simplest and 
oldest form of mining and extracting the precious metal 
is known as — 

Placer mining, which consists of washing the allu- 
vial deposits, sands of rivers, and other earthy matter, 
by which the lighter particles of earth and sand are 
washed away, while the gold in irregular and flattened 
grains by its gravity remains. 

In the early days of California, when rich alluvial de- 
posits were common at the surface, the simplest appli- 
ances sufficed, the most characteristic of which was — 



250 PRACTICAL DENTAL METALLURGY. 

The "pan" a circular dish of sheet-iron, with sloping 
sides about 13 or 14 inches in diameter. The pan, about 
two-thirds filled with pay dirt to be washed, is held in a 
stream or in a pool of water. The large stones separated 
by hand; the pan is given a twisting lateral motion, 
keeping the contents suspended in the stream to remove 
the lighter substances, the heavier gold remaining on the 
bottom. This process is termed panning out. 

The " cradle" is a simple contrivance based upon the 
same principle for treating somewhat larger quantities. 

The " torn " is a sort of cradle with an extended sluice 
placed on an incline. Under certain circumstances mer- 
cury is used in the sluice to amalgamate the gold. 

The "sluice," a Californian invention, is used in work- 
ing on a larger scale, where the supply of water is 
abundant. The simplest form of this consists of a rect- 
angular trough of boards set up on trestles at an inclina- 
tion that the stream of water may carry off all but the 
largest stones, which are kept back by a grating, and 
removed by hand as they accumulate. The floor of the 
sluice is provided with riffles made of strips of wood laid 
parallel with the current, and at other points with boards 
having transverse notches filled with mercury for the 
accumulation of the gold. The length of the sluice 
depends, of course, upon the volume and flow of water, 
the ordinary ones ranging from 100 to 500, and even to 
1000 feet in length, while the sluices leading from 
hydraulic operations are sometimes a mile in length. 

Hydraulic Mining. — This method is also a Californian 
invention, and has for the most part been confined to the 
placer mining of this State. The method is employed 
where an abundance of water is available, and where 
thick banks of auriferous gravel are to be removed; it 
consists in loosening and washing away banks of gravel, 



GOLD. 251 

sand, and soil with powerful streams of water discharged 
from nozzles resembling those of a fire erjgine. It is 
supplemented by the use of gunpowder for breaking up 
and removing "bed rock," immense boulders, etc., and 
arrangements must be made for saving the gold without 
interrupting the flow of water, and for disposing of the 
vast masses of impoverished gravel. The stream from 
the site of operation laden with stones and gravel passes 
into sluices where the gold is recovered in the manner 
already described. 

Quartz mining does not greatly differ from the meth- 
ods employed in the extraction of similar deposits of 
other metals. The quartz is first reduced to a very fine 
powder; this is accomplished in the most productive 
regions, such as California and Australia, by means of 
the stamp mill. In this operation cylindrical iron pestles, 
weighing from 600 to 800 pounds, are lifted by means of 
cams, and allowed to fall some 8 or 10 inches at the rate 
of from 30 to 90 blows per minute upon the quartz. A 
stream of water carries the comminuted material in con- 
tact with mercury, which, on account of its great affinity 
for the gold, absorbs and separates it from the earthy 
gangue. To prevent the " sickening " and "flouring" 
of the mercury, which is produced by certain associated 
minerals in the ore, and which occasions much annoyance 
and some considerable loss of both gold and mercury, by 
greatly diminishing the solvent powers of the latter 
metal, a small quantity of the amalgam of sodium is 
added to the mercury. 

Before the solvent mercury becomes saturated it is re- 
moved and subjected to powerful pressure in leather 
bags, when the excess is squeezed out through the pores 
of the leather, leaving the more or less coherent mass of 
rich amalgam inside. The mass is then heated in a 



252 PRACTICAL DENTAL METALLURGY. 

proper vessel, when the mercury is distilled over and re- 
condensed in iron retorts. The gold is left in a spongy 
state usually quite free from other metals, except silver, 
which is separated by the " parting process," to be sub- 
sequently described. The spongy gold with its silver 
content is then melted in plumbago crucibles with the 
addition of a small quantity of suitable fluxes and shipped 
as bullion. 

In some cases it has been found advantageous to smelt 
the ore by fusing it with lead, which latter in the fused 
state has a very great affinity for gold. In such opera- 
tions the crushed ore is mixed with suitable proportions 
of metallic lead or litharge and charcoal, together with 
some lime or clay as a flux for the silica and fused on the 
hearth of a reverberatory furnace. The melted lead dis- 
solves the particles of gold, just as mercury does, and 
sinks beneath the lighter slag; is drawn off and afterward 
separated from the gold by cupellation. 

Chlorination Process. — Under some circumstances it 
is found best to separate the gold from the quartz in a 
wet way by means of chlorine. The process depends 
upon the fact that chlorine acts rapidly upon gold, but 
does not attack ferric oxide, and is now adopted in Grass 
Valley, California, where the waste minerals, principally 
pyrites, have been worked for a considerable time by 
amalgamation. 

The ore is roasted at a low temperature in a reverbera- 
tory furnace, during which salt is added to convert all 
the metals present, except iron, into chlorides. The 
auric chloride is, however, decomposed at the elevated 
temperature, and the finely divided particles are readily 
attacked by the chlorine gas. The roasted mineral, 
slightly moistened, is then introduced into a wooden vat 
which is provided with a double bottom. Chlorine gas 



gold. 253 

is led from a generator beneath the false bottom, and 
rises through the moistened ore, converting the gold into 
a soluble chloride which is afterwards removed by wash- 
ing with water. The noble metal is then precipitated by 
the sulphate of iron. The method is very accurate and 
yields metal of great purity. 

REFINING GOLD.— The accumulation of gold in 
the form of scraps, filings, etc., in the dental laboratory 
and operating-room frequently becomes a source of con- 
siderable loss to the dentist, on account of unfamiliarity 
with the methods of refining, and lack of convenience 
and apparatus necessary to its several processes. 

Some forms of scrap-gold, such as old fillings, need 
only to be melted with. the proportion of silver, copper, 
or both, to produce the desired alloy. Others, as scrap- 
plate of known carat, may be utilized by simply remelt- 
ing and rolling. 

Old crowns, plates, bridges, mixed filings containing 
more or less iron from the file, zinc, lead, antimony, and 
other base metals may be converted into malleable gold 
by simply roasting with such fluxes as will combine 
chemically with the base metals and remove them. 

Sweepings may be washed and then carried through 
the same process, which is known as 

THE ROASTING PROCESS.— A method for roughly 
refining and rendering brittle gold malleable. This pro- 
cess may be most satisfactorily employed where the ap- 
proximate carat of the bulk of the scraps is known and 
the gold is suspected to be unworkable, owing to the 
admixture of base metals. 

The larger pieces should be removed from the accu- 
mulation and the smaller ones with the filings freed from 
as much iron and steel as possible by a good magnet. 
All should then be placed in a previously well-boraxed 



254 PRACTICAL DENTAL METALLURGY. 

and tried graphite crucible, with the addition of sufficient 
potassium carbonate to well cover the charge; the object 
of this addition being to form a thin flux, permitting the 
small particles and filings to sink and accumulate in one 
mass. 

The furnace should be placed beneath a fume-chimney 
or by a window with an outward draught, that the fumes 
escaping from it during the roasting may not fill the 
laboratory, thereby endangering the health of the students 
or operator and damaging such instruments and tools as 
may be unprotected. The most convenient place to avoid 
such results is the fire-place. The furnace may be placed 
beneath its chimney in such a manner that all fumes will 
be readily carried off. 

When the metal has become thoroughly fused, the 
refining process may be begun by first adding small 
quantities of the oxidizing agent, potassium nitrate, 
(KN0 3 ), accompanied with borax as needed to properly 
protect the mass and further the process. The object of 
the potassium nitrate is to furnish sufficient oxygen to 
oxidize the contaminating base metals beneath the flux, 
thus separating them from the gold. As most base 
metals are easily oxidized under these circumstances, a 
continuation of this process from ten minutes to one 
hour and a half, according to the quantity of material, 
and the proportion of base metals contained, adding the 
niter and borax as required, and maintaining a perfect 
fusion of the metal, the ingot, when made by pouring 
into a previously warmed and oiled mold, will be found 
to be quite malleable. 

If, however, upon examination it is found to be still 
brittle, it should be placed in a clean, boraxed, and tried 
crucible, heated, and brought to a perfect state of fusion. 
A mixture of equal parts of finely pulverized vegetable 



gold. 255 

charcoal and amnionic chloride should then be added; at 
first sufficient to properly cover and protect the molten 
mass and afterwards a small quantity at a time as it is 
needed. When the metal has been sufficiently treated, 
which may be determined by removing small quantities 
and subjecting them to the physical tests for malleability, 
the crucible is to be removed from the furnace and the 
metal cast into an ingot or allowed to cool in the crucible 
as a button. 

The rationale of such a process is that the heat of the 
crucible breaks up the chloride compound, liberating the 
chlorine in the nascent state; which in turn combines 
with the metals lead, tin, and silver contained in the 
gold to form chlorides respectively. These are either 
volatilized or taken up by the flux, the gold remaining 
free of them. 

Mercuric chloride is sometimes used when the contam- 
ination of the gold with lead or tin is extensive, or where 
it is desired to remove a quantity of silver. But its use 
is so dangerous on account of the fumes evolved it is 
rarely employed. 

Sulphur or antimonic sulphide is used to abstract large 
quantities of silver from gold, by combining with the 
former to form the fusible sulphide of silver, leaving the 
gold free, or if the antimonic sulphide has been used, 
contaminated with antimony, which may be removed by 
fusing with borax and potassium nitrate, as previously 
described. 

In the process of refining by fluxes, the first step 
should be to determine, as far as possible, the nature of 
the debasing elements; this being known or reasonably 
approximated, the process may be confined to the par- 
ticular flux most likely to free the gold from its contam- 
ination. Iron, steel, zinc, copper, antimony, and bismuth 



256 PRACTICAL DENTAL METALLURGY. 

are, perhaps, best removed by oxidation through the 
agency of potassium nitrate. Lead, tin, and silver are 
removed by chlorine, forming volatile compounds with 
that element. 

If, after such treatment, the alloy is found to be malle- 
able, but stiff or elastic, or dull in color, it very probably 
contains some platinum which cannot be removed by this 
means, but which may be gotten rid of by a wet method. 
When desired, such an alloy may be made direct use of 
as clasp gold. 

When the object is to produce pure gold from which to 
subsequently prepare desired carats by alloying the result, 
it is best and most conveniently attained by the process 
known as 

PARTING GOLD.— A wet method for refining gold 
by inquartation, or "quartation," as it is more commonly 
known. This is accomplished by digesting the thinly 
rolled or granulated alloy of silver and gold in either 
nitric or sulphuric acid. 

The student, in his choice of metal for this operation, 
may endeavor to obtain gold containing as much silver 
as possible, and, as this will require an additional 
quantity of the latter metal fused with it in order to 
carry out the operation, it is of course an object, if pos- 
sible, to employ silver which contains small quantities of 
gold, and thus, as it may be said, to carry on a double 
refining process at once. 

As the actual separation of the two is effected by 
digesting the mixture in hot nitric acid, which, while it 
is a ready solvent for other metals, is inactive upon gold, 
it may be asked: Why not at once treat the alloy with 
acid without such alloying ? Such would be quite use- 
less, for, the foreign metals being in so small a relative 
proportion, the acid would only remove the alloy at or 



GOLD. 257 

near the surface, the metal being sufficiently close in 
texture to mask all the rest from the action of the acid. 

The sulphuric acid process is doubly recommended, 
especially when large quantities of the alloy are to be 
digested, as it is less expensive, and the gold is obtained 
of a greater degree of fineness. The oxidizing action of 
the nitric acid is of especial value, however, when tin or 
antimony is present in the batch of metal. 

Preparation of the Alloy. — The impure gold is first 
weighed and the approximate weight of the silver, if it 
contains any, subtracted; silver is then added in the pro- 
portion of three to one, less the amount already contained 
in the alloy, thus when melted forming an alloy of 
three parts silver and one part impure gold. Hence 
the term " quartation." These proportions are then 
fused together in a clean and boraxed crucible, well 
mixed, and either poured into warmed and oiled ingot- 
molds, to be subsequently rolled, or dropped while molten 
from the crucible into a wooden tub or tank of cold water 
for the purpose of granulation. The latter is unques- 
tionably the simplest method of preparing it for the digest- 
ing process, for, if poured into the ingot-molds, the alloy 
will require rolling to a very thin ribbon (No. 35 gauge), 
after which it must be cut into small pieces. The roll- 
ing many times is impossible, because of the gold that it 
is desired to refine being exceedingly brittle. The alloy 
being thus prepared, is ready for the acid. 

Nitric Acid Process. — For this process the prepared 
alloy is placed in a Florence flask and nitric acid to the 
amount of about one and one-half times the weight of the 
alloy poured on. The acid should always be tested for 
chlorine by adding a drop of the solution of silver nitrate 
(AgN0 3 ) to it, which, if chlorine be present, will in- 
stantly be rendered milky from the precipitated chloride 



258 PRACTICAL DENTAI, METALLURGY. 

of silver. Heat the flask gently in a sand-bath over a 
Bunsen or alcohol flame. Copious red fumes of the 
oxides of nitrogen and ammonium will be given off, show- 
ing vigorous action on the alloy, and the silver and other 
metals will be dissolved, leaving the gold in a spongy 
mass of a blackish-brown color. When this evolution 
has entirely ceased and the flask is clear, carefully decant 
the solution of the nitrates of silver, etc., thus formed 
and preserve it, adding a fresh portion of nitric acid 
and boil until all fumes cease to rise, which marks the 
termination of the digesting process. The acid is 
now replaced by distilled water two or three times, 
for the purpose of washing the gold remaining. At 
length filter the contents of the flask, catching the gold 
on the filter paper, add a sufficient quantity of potassium 
carbonate, fold the paper over the whole, and place in a 
previously boraxed crucible, melt and pour into warmed 
and oiled ingot-molds. 

Gold thus refined may reach 998-1000ths fineness, and 
is ready for any desirable alloying. 

For the recovery of the silver, see chapter on that 
subject. 

Sulphuric Acid Process. — The use of sulphuric acid 
for the operation is preferred by many. For, as was 
stated, it is more economical; and the gold so reSned is 
more thoroughly freed from silver; indeed, it is said that 
gold having been previously refined by the means Of 
nitric acid may be freed of still more silver by this acid. 
In operating the metals are so mixed that the gold 
amounts, at most, to not quite half the weight of the 
silver; and if copper is contained, (which in small propor- 
tions facilitates the operation), it should be under 10 per 
cent, for, if too much be present, a large quantity of 
sulphate of copper will be formed, which latter is insolu- 



GOLD. 259 

ble in the strong acid liquors. The process may be 
employed for silver containing very small quantities of 
gold. Thus, in France, it was found very profitable to 
separate the gold from old five-franc pieces, which con- 
tained only l-1000th to 2-1000ths of gold. 

The alloy having been granulated, as before described, 
is introduced into a digester (Florence flask) with about 
two and one-half times its weight of concentrated sul- 
phuric acid. This is allowed to boil, during which strong 
action is evidenced by copious evolution of sulphur 
dioxide, while the silver and copper are simultaneously 
converted into sulphates. This first boiling is continued 
as long as sulphur dioxide is evolved, which in large 
quantities of metal will commonly go on about four 
hours. The liquid is then removed and a smaller quan- 
tity of acid added, the boiling being further carried on 
for a short time, after which the digester is allowed to 
remain at rest, in order that the gold may subside. 
Sometimes it may be requisite to use even a third acid. 

Repeated washing of the gold with boiling water is 
now necessary, as the sulphate of silver is a very insoluble 
salt, and sulphate of copper, when contained in so 
acid a menstruum, is also somewhat so. The gold is 
then dried, melted, and poured, as described before. 

This process affords gold as pure as 998.5-1000ths. 

THE PREPARATION OF CHEMICALLY PURE 
GOLD. — The metal, either, in the form of powder, gran- 
ulations, thin plate, or "cornets" from the purest gold 
that can be obtained, is dissolved in chemically pure 
nitro-hydrochloric acid.* The best material to operate 
on is gold which has been refined in the ordinary 
way; this may be used in the form of a powder, as it is 

* One volume of nitric to two of hydrochloric acid, (or any proportion, so 
the latter is in excess). 



260 PRACTICAL DENTAL METALLURGY. 

precipitated in the last process, as granulations or as 
plate. The acid for small quantities is best contained in 
an evaporating dish placed in a sand-bath upon a tripod, 
over the flame of a Bunsen burner, beneath a chimney 
or near an open window. The action will be tolerably 
energetic when the metal is first introduced; hence, it is 
not necessary to ignite the burner at the start, but as the 
action slackens a moderate heat may be applied. 

Instead of previously mixing the acids, the hydro- 
chloric acid may first be poured over the metal, and the 
nitric acid afterward gradually added in small portions, 
the function of the nitric acid being to oxidize the hydro- 
gen of the hydrochloric acid, converting it into water, 
while the chlorine, which is the active solvent, is 
liberated in the nascent state and unites with the gold, 
converting it into auric chloride, which dissolves.* 

Bach ounce of gold will require about three and one- 
half ounces of mixed acid for its solution. During the 
process of solution a sediment will be noticed in the bot- 
tom of the evaporating dish, which will be recognized 
by the operator as a silver chloride, formed .by the union 
of the silver contained in the gold and the liberated 
chlorine. It must not be expected that all the silver will 
be directly precipitated to the bottom as a chloride, for 
the liquor is strongly acid, and some may be held in solu- 
tion. Therefore, this must be taken into consideration, 
and subsequent pains taken to throw it down by the 
thorough evaporation of the nitric acid. The gold hav- 
ing been dissolved, the solution is now best transferred 
to a clean dish by decantation, leaving the chloride of 
silver in the first and the solution contained in the 
second dish heated to further evaporate. When about 
one-third is evaporated more chloride of silver will be 

* Dr. E). C. Kirk, American System of Dentistry. 



GOLD. 261 

found to have been separated from the solution and 
precipitated. It is well, therefore, to again transfer the 
solution to a third dish by decantation and evaporate as 
before, care always being maintained during the heating 
not to apply so great a temperature as to decompose the 
auric salt. 

As the bulk is reduced over the gentle heat by evapora- 
tion, small quantities of hydrochloric acid are to be 
added from time to time, which has the effect of liberat- 
ing nitrous anhydride by decomposing the remaining 
nitric acid in the liquor; these additions must, however, 
be made very cautiously, for the action produced is very 
energetic, and, without due precaution, considerable por- 
tions of the now rich liquor will be spirted out of the 
dish and lost. When the liquor has become of a deep 
red color, and of the consistency of syrup, it is to be 
withdrawn from the heat and permitted to rest for a time, 
when the whole of the auric chloride will crystallize, 
forming a mass of prismatic crystals.* 

The bottom of the dish is now carefully wiped off to 
remove any sand or dirt that may have collected there 
from the sand-bath, and the dish and its contents im- 
mersed in about a half pint of distilled water, acidu- 
lated slightly with hydrochloric acid. It is better now 
to let this solution stand a week, for chloride of silver, 
although slightly soluble in a very strong and hot acid 
solution, is separated by dilution, and, by allowing this 
rest, it will completely subside in the vessel. At the 
end of this time the solution must be filtered to remove 
any foreign substance, together with the silver chloride. 
The filtrate will then be seen to be a rich straw-yellow, 
and the gold it contains is ready for precipitation. 

* Makins' Metallurgy. 



262 PRACTICAL DENTAL METALLURGY. 

Precipitating the Gold. — The solution is now best 
contained in a large glass flask, and the precipitating 
reagent added. As gold is one of those metals which, as 
a base, combines with very feeble affinities, it is conse- 
quently not only very easily separated, but the physical 
conditions of the precipitate may be much modified and 
controlled by the nature of the precipitant, as also by the 
mode of operating. Thus gold may be thrown down in 
a powder, in scales, in more or less of a crystalline state, 
in a tolerably compact sheet or foil, or lastly, in a spongy 
condition. And these states may be attained with some 
degree of certainty, although the circumstances determin- 
ing the more compact forms are hardly yet well under- 
stood. 

Spontaneous precipitation may take place to some ex- 
tent in a vessel of trichloride of gold when exposed to the 
air; and thus the sides of the vessel containing it will 
slowly become covered with the deposit. This is prob- 
ably due to the action of the nitrogen of the air. Many 
elementary substances will precipitate gold from the tri- 
chloride. Most of the lower metals reduce it, some 
metallic salts throw it down, and many organic bodies 
readily precipitate it. Thus sugar when boiled in it gives 
a first a light red precipitate, which afterwards darkens 
in color.* 

Practically, however, ferrous sulphate or oxalic acid 
are the only precipitants used. The oxalic acid is pre- 
ferred, and is an excellent precipitant. 

The gold salt, being in solution, is broken up by the 
addition of a strong solution of oxalic acid, and the gold 
is precipitated to the bottom as either a crystalline mass 
or a leafy foil. It is necessary to add a slight excess, 
and the whole should be kept at a gentle heat in a sand- 

* Makins' Metallurgy. 



GOLD. 263 

bath over a flame. Soon after the application of heat 
some slight bubbling is noticed, a copious evolution of 
gas takes place, and at the same time the body of the 
liquid appears filled with most delicate spangles of me- 
tallic gold, which become coherent as they descend, and 
in consequence assume most any one of the forms above 
mentioned. The gas noticed to escape is C0 2 , from the 
compound, oxalic acid. The reaction is of the simplest 
— an acid on a binary salt — 

2AuCl 3 + 3C 2 H 2 4 =6HC1+ 6C0 2 + 2 Au. 

"The action of this precipitant being gradual, and 
capable of much regulation, by the amount and nature 
of heat employed, while it is also peculiar in being at- 
tended throughout by this evolution of gas which rises 
quickly through the solution, there is produced from the 
former cause a tendency in the metal to deposit in a 
crystalline or crystallo-granular state; while from the 
latter a more or less spongy character is given to it: 
hence it will be readily seen that inasmuch as we are able 
to modify these conditions, so we can in the same degree 
influence the molecular nature of the result."* 

Where ferrous sulphate is used about four times the 
weight of the gold will be necessary for precipitation. 
This may be dissolved quickly in hot distilled water and 
added to the gold solution. The precipitate thrown 
down is of a brown color, and will, on being gently 
burnished with the finger-nail, assume that metallic 
golden luster characteristic of the metal. The following 
is the reaction — 

2 AuCl 3 + 6FeS0 4 =Fe 2 Cl 6 + 2Fe 2 (S0 4 ) 3 + 2 Au. 

After the solution has fully subsided from the disturb- 
ance caused by addition and precipitation a quantity of 

* Makins' Metallurgy. 



264 PRACTICAL DENTAL METALLURGY. 

hot hydrochloric acid may be added, and much of the 
supernatant liquor removed, either with a siphon or by 
decantation, and the remainder of the solution and pre- 
cipitate poured upon the filter paper. The precipitate 
is afterwards washed with hydrochloric acid, distilled 
water, aqua ammonia, and again with distilled water. 
The necessity of this is apparent, especially in the use 
of ferrous sulphate as the precipitate will become more 
or less contaminated with the iron, and in the use of 
oxalic acid to remove the copper, as gold precipitated by 
oxalic acid from an acid solution containing copper is 
always contaminated with cupric oxalate. It is then 
also advisable to heat the solution with a slight addition 
of potassium carbonate, a soluble double oxalate of copper 
and potassium is formed, and the gold is left in the pure 
state. Gold may also be precipitated from its acid solu- 
tion in a state of purity in the form of brilliant span- 
gles by means of hydrogen dioxide, thus — 

2AuCl 3 + 3H 2 2 =-6HCl+60 + 2Au. 

When the precipitated gold has been carefully washed 
and re-washed with distilled water, and the above-men- 
tioned reagents, it may be dried and placed in a new 
crucible, previously boraxed, with some potassium car- 
bonate and potassium nitrate melted and cast into an 
ingot. If iron ingot moulds are used the gold should be 
washed after moulding in hot hydrochloric acid to remove 
any trace of metallic or oxide of iron that may by chance 
have adhered to its surface during the process of casting 
the ingot. 

EXPERIMENT No. 68.— Each student should provide himself with not 
less than two and a half pennyweights of gold or alloy (old jewelry, etc.) con- 
taining that amount; accurately weigh and describe it. If malleable, the 
instructor may add small quantities of base metal to destroy its malleability, 
acquainting the student with the weight and character of debasing metal used. 
The alloy should then be roasted by the student, as described in the process, 



gold. 265 

until malleable, after which the button or ingot should be alloyed with three 
times its weight of silver and carried through the parting process. The result 
of this operation is then to be rendered chemically pure by the third process 
described, then cast into a smooth ingot and rolled (between parchment or 
Swedish filter paper, with frequent annealing, exercising care to keep it pure 
and clean) to No. 60 or 30 foil, which is to be inserted in a tooth as a filling. 

PROPERTIES.— Pure gold is a rich, beautiful, yellow 
color, of strong metallic luster, unalterable in air. It is 
the most ductile of all metals, but ranks only fifth in 
point of tenacity. One grain, however, if covered with 
a more teuacious metal, like silver, forming a composite 
wire, may be drawn into a wire 550 feet in length, and 
only l-5000th of an inch in diameter. It is also the 
most malleable of all metals. One grain of it may be 
beaten into leaves so thin as to cover an area of 75 
square inches, being of but l-370,000th of an inch in 
thickness. 

Very thin leaves of gold appear green in color by 
transmitted light; but when heated, the light trans- 
mitted is ruby-red. 

Gold possesses the property of welding cold. Thus, 
thin leaves, foil, and other forms of gold are more espe- 
cially adapted to the use of the dentist as a filling ma- 
terial. The small particles are welded together in one 
perfectly homogeneous mass as the plug is inserted. The 
finely divided metal, such as that thrown down in the 
preparation of pure gold from the chloride solution, may 
be compressed between dies in the form of disks or 
medals. 

The pure metal fuses at 1100° C. or 2012° F., and its 
alloys at much lower temperatures. When heated much 
above its melting point it slowly volatilizes and is readily 
dissipated in vapor by the oxyhydrogen flame. 

Pure gold is nearly as soft as lead, in consequence of 
which articles of jewelry, coin, etc., made from it are 



266 PRACTICAL DENTAL METALLURGY. 

alloyed with copper, silver, platinum, etc, to give them, 
the requisite hardness, durability, and elasticity. 

The specific gravity of gold cast in an ingot is 19.265; 
when stamped, 19.31; and that of the precipitated metal 
from 19.55 to 19.72. 

Graham has shown that gold is capable of occluding 
0.48 of its volume of hydrogen, and 0.2 of its volume of 
nitrogen. 

GOLD BEATING.— After the gold is precipitated 
from the chloride solution it is thoroughly washed, dried, 
and melted in a clean crucible at a temperature higher 
than necessary to simply fuse it, by which its mallea- 
bility is said to be improved. It is then poured into 
ingot-molds previously heated and oiled, and cast into 
ingots, each one inch wide, one-fourth of an inch thick, 
and from four to eight inches in length. These are re- 
moved from the mold, cleaned in dilute sulphuric acid, 
washed, and annealed. The ingot is next laminated by 
being repeatedly passed through heavy steam rollers, and 
annealed after each lamination, until it is formed into a 
ribbon one inch wide, about the thickness of tissue paper, 
and its length depending upon the original weight of 
the ingot. 

The ribbons are then cut into pieces of an inch square, 
their thickness depending upon the number of the foil, 
2, 4, 6, 10, etc., it is designed to prepare from them; some 
allowance being made for subsequent trimming, and 
the necessity for leaving the sheet of correct weight. 
These little squares are again cleansed, taken up by 
wooden pliers and placed between the leaves of a 
(l cutch " made from vellum or ground parchment which 
holds about two hundred pieces. The cutch is then 
enclosed in parchment bands and beaten on a granite or 
marble block, securely and firmly set, with a hammer 



GOLD. 267 

weighing from seventeen to twenty pounds. The ham- 
mer is short-handled, and is wielded by the beater with 
one hand, while with the other hand he holds and rotates 
the packet of gold. 

Every few moments the cutch is opened and the gold 
examined; then split in half and the position of the 
pieces reversed, so as to bring the middle ones to the out- 
side and those on the outside to the middle of the packet. 
During the beating the packet is continually rotated and 
turned, to distribute the force of the blows equally 
throughout the packet; at intervals it is taken up and 
rolled between the hands to overcome any adhesion that 
may have taken place between the leaves of metal and 
interposed parchment. 

Considerable skill is required to produce a good quality 
of foil, the physical properties of the metal being capable 
of alteration by the too great rapidity of the process. 

When the gold is beaten into sheets about three or 
three and a half inches square, or about the size of the 
leaves of the cutch, which requires from fifteen to twenty 
minutes, they are removed from the cutch by means of 
the wooden pliers, and placed piece by piece in a second 
packet of larger size made of the same material and 
called a " shoder." If, however, the pieces are too thick 
to produce the required number they are cut into four 
pieces, and the process repeated in the cutch. The 
shoder is then placed in the parchment bands, and the 
beating continued until the gold again equals the size of 
the skins, which requires about twice the length of time 
as before. 

After the last beating the pieces are carefully laid out 
one at a time on a calf-skin cushion lined with soft flannel; 
the blemished, broken and torn ones are laid to one side, 
and the perfect ones are cut into uniformly square sheets 



268 PRACTICAL DENTAL METALLURGY. 

so familiar to the dentist, by means of an instrument 
carrying four edges of malacca reed called a wagon. The 
gold does not adhere to this as it does to the metal. 
The sheets are then accurately weighed and are ready 
for annealing. 

The annealing is an important and delicate process, 
and may be accomplished in several ways: in the muffle 
of a furnace, on heated platinum, or on platinum- wire 
gauze with a spirit-lamp beneath it. Whatever may be 
the means by which it is accomplished, it must be prop- 
erly done, i. e., the temperature must be sufficient to 
thoroughly heat and soften it uniformly in every part of 
the sheet, without melting and thickening the edges. 

From the first to the last step the most important con- 
sideration is absolute purity and cleanliness. 

Kach book of gold foil contains }i of an ounce, 2}4 
pennyweights, or 60 grains. Each full sheet is 4 inches 
square, and the number of the foil indicates the weight 
of each full sheet. Thus, a book of No. 2 would contain 
30 sheets, 4 inches square, of 2 grains each; No. 10, 6 
sheets of 10 grains each; No. 30, 2 sheets (4 inches 
square) of 30 grains each, and so on. 

Corrugated foil is supposed to have been an outcome 
of the great Chicago fire. When the safes of one of the 
depots were opened, it was found that the paper had 
burned to a crisp, and the foil in the form of what is now 
known as corrugated foil. It was tried by some, and 
found many friends. In making the corrugated foil 
to-day a miniature Chicago fire is used to burn the 
paper. The gold is beaten as described before to No. 4 
foil. It is then placed, sheet by sheet, between paper 
and enclosed in an iron box, with weights on the gold. 
The iron box is then placed on a slow fire and allowed to 
smolder, care being taken not to ignite the paper. After 



gold. 269 

smoldering, the heat is gradually let on until the 
paper becomes carbonized. As the paper shrinks, the 
gold shrinks with it. The carbon is then blown off, 
sheet by sheet, and we have what is called corrugated or 
crystalline gold. 

Cylinders. — These sheets are then rolled upon them- 
selves in a cylindrical form of desired thickness, and cut 
into the size and style of cylinders required. 

The numbering of pellets or cylinders is so variable 
with the different manufacturers that it really means 
little, if anything. Some number them as follows: No. 
%, one-fourth of a sheet of No. 4 foil, rolled and cut 
into pellets of varying length; No. ^, one-half of a 
sheet of No. 4 foil, rolled and cut into pellets; No. 1, a 
whole sheet of No. 4, and so on. The length of the 
pellets is also variable, and is designated as style A, B, 
C, etc., by some manufacturers.* 

Cylinders are, in accordance with the manner in which 
they are rolled, known as loose and compact. 

The former can only be made by the manufacturers, 
and are composed of several sheets of No. 4 corrugated 
cohesive foil laid loosely upon one another and rolled 
lightly around a smooth needle-like piece of steel. The 
needle is then removed and the cylinders are cut by a 
peculiar sharp tool into assorted sizes or styles. 

The compact variety may be made by the operator in 
a similar manner, except that the ends of the cylinder 
will necessarily be more compact, on account of the 
manner in which it is cut. 

There are other forms of gold used, such as mat, block, 
rope, tape, ribbon, etc. 

Rolled Gold.— The heavier foil, as Nos. 20, 30, 60, 
160, etc., is usually prepared by rolling, instead of 

* Hood and Reynolds. 



270 PRACTICAL DENTAL METALLURGY. 

beating. Flattening by rolling elongates the fiber, 
instead of increasing its surface in all directions, 
and it is thought produces a foil of greater density 
and toughness, and, when annealed, greater softness. 
Such foil is exceedingly cohesive and tenacious. It is 
also made in the non-cohesive variety. 

Gold and Platinum Foils. — These are prepared in a 
variety of ways by several manufacturers of dental foils. 
Dr. C. E. Blake of San Francisco prepares a weldable, 
tenacious, platinum foil by electro-depositing a surface 
of pure gold upon it. As a rule such combinations pro- 
duce a filling more able to stand the stress and abrasive 
force of mastication. 

Crystal Gold. — This form of gold was first introduced 
by A. J. Watts, who prepared it by precipitating gold 
from a chloride solution by means of oxalic acid, treating 
the precipitate with nitric acid and neutralizing the acid 
by washing with ammonia. The crystalline substance 
was then thoroughly dried in a muffle, when it was 
ready for use. The preparation fell into disuse on 
account of its unreliable quality, frequently being con- 
taminated with nitric acid and other foreign substances. 
It is now prepared by electrolysis from the chloride solu- 
tion. Plates of pure gold are suspended in the solution 
w T hich replace the metal as fast as it is deposited upon the 
platinum cathode. When prepared properly it is an 
unobjectionable material, but certain precautions must 
be observed in its use, as its manipulation is very 
deceptive. 

ANNEALING GOLD.— This process has a two-fold 
purpose: (1) To remove any deleterious substances 
which may have accumulated on the gold through ex- 
posure, and (2) to soften and more perfectly secure its 
cohesive quality. 



GOLD. 271 

After gold has been exposed for some time to the 
action of the air and extraneous influences, it loses to a 
great extent, the qualities it possessed when first pre- 
pared,^ e., it looses its softness, cohesiveness, etc., but is 
partially, if not wholly, restored to its original condition 
by annealing. 

This is accomplished by a variety of methods. The 
main consideration, however, is the employment of a 
flame of as great purity as possible, free from the evolu- 
tion of such substances as sulphur, chlorine, phosphorus, 
carbon, and their compounds. Obviously, flames from 
substances as free as possible from such compounds are 
the best; the desideratum being a pure hydrocarbon, 
which, all things being considered, is most conveniently 
found in good alcohol. 

The gas flame from a small Bunsen burner is one of 
almost perfect combustion; has become quite popular, 
and may be conveniently used where the gold is not 
annealed by passing through the flame. The most desir- 
able means, perhaps, is found in the pure platinum coils 
which are heated to incandescence by the electric current. 

It has been observed that more even and uniform 
results may be attained by annealing the gold in small 
quantities on heated mica, or platinum, since the por- 
tion of the pellet or foil held by the carriers is only 
slightly heated when passed through the flame. Gold is 
best annealed after cutting, as the action of the shears in 
cutting annealed foil tends to give ita " wire " edge by 
slightly condensing it. 

PROPERTIES OF GOLD FOIL .—These are various 
and variable with the products of different manufac- 
turers. The most prominent and important for the 
consideration of the dentist is that known as cohesiveness. 



272 PRACTICAL DENTAL METALLURGY. 

Most metals which possess the analogous property 
called weldability are weldable in proportion to the 
length of time they will remain in a plastic condition 
under heat without melting, but pure gold is weldable 
cold. It is not to be inferred that gold is the only metal 
which is weldable cold; on the contrary, the clean, 
pure surfaces of many metals, such as lead and copper, 
are quite coherent, but much difficulty is encountered in 
obtaining and keeping them in the necessarily pure 
state. 

Gold prepared by the manufacturers is unfortunately 
given a variety of names, such as cohesive, semi-cohe- 
sive, non-cohesive, hard, soft, etc., all of which relate 
to its property of cohesiveness, and are perplexing and 
misleading to the older practitioners, not to say students. 
Gold is either cohesive or non-cohesive. 

Cohesive gold is simply pure gold. The greater its 
purity, the more perfect its cohesiveness. It is annealed 
and soft when it leaves the makers, and sheets of it laid 
upon each other will cohere by mere contact. As stated 
previously, after it is exposed to air and to extraneous 
influences, handled and jostled about, it loses, from con- 
tact with impurities, some of its cohesiveness, and from 
pressure, some of its softness. These two properties are, 
however, partially or fully restored by proper annealing. 

Non-cohesive Gold. — Since pure gold is cohesive by 
virtue of its purity, it is obviously conversely true that 
non-cohzsive gold is as it is from /^purity. The process 
of preparing non-cohesive gold is a trade secret which 
every manufacturer possesses as part of his stock in 
trade. The natural cohesiveness of gold may be over- 
come by slightly alloying with iridium or iron, but it is 
probable this property is generally destroyed by some 
surface treatment the foil receives. Hastings & Co. pre- 



gold. 273 

pare a very excellent non-cohesive foil, which, from 
analysis has been found exceedingly pure. The process 
of manufacture is not known, but is probably dependent 
upon some surface treatment. Non-cohesive foil cannot 
be made cohesive by annealing, because the impurity 
cannot be removed by that means. 

Semi-cohesive foil is non-cohesive before and co- 
hesive after annealing. It is evident that the process of 
annealing purifies it, thereby restoring its natural prop- 
erty. 

The terms "'hard" and ''soft" are used by the makers 
and many practitioners to designate the cohesive and 
non-cohesive varieties, respectively. These terms are, 
however, erroneous, and should not be used. 

" The feeling of softness," says Dr. Kirk, " exhibited 
by non-cohesive foil under the instrument is due largely 
to the fact of its non-cohesiveness, whereby the several 
laminae slip or slide one upon another, thus conveying a 
yielding or soft sensation to the tactile sense, and making 
it possible to condense large masses at a time, the pres- 
sure being conveyed continuously throughout the mass 
and the condensation or consolidation being uniform. A 
similar mass of cohesive foil, treated in the same manner 
and under like conditions, presents a greater resistance 
to the instrument, and conveys the idea of hardness, 
from the fact that as pressure is applied the successive 
laminse unite or weld together from the surface down- 
ward into a homogeneous stratum of metal, which offers 
greater resistance and becomes more impenetrable by 
constant additions to its thickness; until the condensing 
instrument fails to make any further impression; but 
upon removing the mass of gold it will be found that 
that portion of it which occupied the bottom of the 
cavity is still in the form of foil and not homogeneously 
condensed." 

Purity. — The physical properties of gold are more 
apt to be influenced by lack of purity than by any other 



274 PRACTICAL DENTAL METALLURGY. 

factor. Impurity may be occasioned by several means: 
first, by admixture of other metals, especially those 
easily oxidized. Second, by surface contamination 
caused by handling or exposure to vaporous gases. 
Third, by the absorption or occlusion of gases. 

The following assays were made for Dr. Kirk by 
Messrs. Dubois and Hckfeldt, assayers of the United 
States Mint, Philadelphia. The table exhibits in thou- 
sandths the relative fineness of some of the foils in 
general use.* 

Bach assay was duplicated: 

No. 1. Abbey's Non-Cohesive 998.8 998.7 

No. 2. Wolrab's, from C. A. Timme. . . 999.2 999.3 
No. 3. Quarter-Century, S. S. White 

Dental Mfg. Co 999.1 999.1 

No. 4. Rowan's Decimal Foil from 

Gideon Sibley 999.9 999.8 

Discoloration. — The unfortunate discoloration of some 
gold fillings is in all probability due to a slight admixture 
of iron obtained during the precipitation from the chlor- 
ide solution when ferrous sulphate is used, or from the 
iron ingot-mold, or from the surface of the plugger-poirit 
during the insertion of the filling. 

COMPOUNDS OF GOLD WITH OXYGEN.— 
Gold forms two oxides: 

Aurous Oxide, or Monoxide, Au 2 0, is prepared by 
adding a solution of caustic potassa to the monochloride. 
It is a green, unstable powder, being easily decomposed 
into metallic gold and auric oxide. 

Auric Oxide, or Trioxide, Au 2 3 , is prepared by 
adding magnesia to auric chloride; when the sparingly 
soluble aurate of magnesium thus formed is well washed 
and digested with nitric acid, auric oxide is left as an 

* American System of Dentistry, Vol. Ill, p. 842. 



GOLD. 



275 



insoluble reddish-yellow powder. It is easily reduced 
by heat or mere exposure to light; soluble in nitric, 
hydrochloric, and hydrobromic, and insoluble in hydro- 
fluoric acid. Its acid properties are marked: it dissolves 
freely in alkalis. When digested with ammonia, it 
yields — 

Fulminating Gold. — This compound is usually pre- 
pared, however, by the addition of ammonia to trichloride 
of gold. It is a buff precipitate, and explodes violently 
when gently heated. Its formula is probably — 

Au ? 3 4H 3 N.H 2 0. 

ACTION OF ACIDS ON GOLD .-Gold is not 
tarnished or affected by air or water at any temperature, 
nor by sulphuretted hydrogen. 

Neither is it soluble in sulphuric, nitric nor hydro- 
chloric acid. 

In nitro-hydrochloric acid, however, it speedily dis- 
solves, forming the trichloride of gold, AuCl 3 . 

It is also attacked by a vapor or solution of chlorine; 

By bromine, dissolving in bromine- water to form 
auric bromide, AuBr 3 ; and 

By iodine, dissolving when finely divided in hydriodic 
acid by aid of the air and potassium iodide, forming 
potassium auric iodide — 

2Au + 6HI + 2KI+30=2KIAuI 3 + 3H 2 0. 

Potassium cyanide solution dissolves precipitated 
gold with the aid of air, forming potassium aurocyanide — 

2Au+4KCN+0=2KAu(CN) a + K a O. 

Purple of Cassius. — So named from its color and 
discoverer. It is much employed for imparting a rich 
red or reddish purple to glass and porcelain, and is of 
especial interest to dentistry, because it is used by the 



276 PRACTICAL DENTAL METALLURGY. 

manufacturers of artifible teeth to produce the gum tint 
of dental porcelain. It is a vitrifiable material composed of 
gold, tin and oxygen. The proportion, however, is 
thought to be variable. It is generally given the formula — 

Au 2 O.Sn0 2 ,SnO.Sn0 2 .4H 2 0. 

It is prepared by a variety of methods. Pelletier's is 
as follows: 20 grains of gold are dissolved in 100 grains 
of aqua regia containing 20 parts nitric to 80 parts com- 
mercial hydrochloric acid; the solution is evaporated to 
dryness over a water-bath; the residue dissolved in 
water; the filtered solution diluted with seven or eight 
deciliters of water and tin filings introduced into it. In 
a few minutes the solution becomes brown and turbid 
and deposits a purple precipitate, which merely requires 
to be washed and dried at a gentle heat. The purple 
thus prepared contains, in 100 parts, 32.746 parts of 
stannic acid, 14.618 of protoxide of tin, 44.772 of aurous 
oxide, and 7.864 of water. The precipitate obtained by 
the addition of stannous chloride to auric chloride is 
always brown. To obtain a fine purple precipitate the 
auric chloride should be treated with a mixture of stan- 
nous and stannic chlorides. 

The purple is now produced by a dry method, by the 
manufacturers of gum enamel. It consists of digesting 
an alloy of gold, tin, and silver in nitric acid. The 
method was discovered by the late Professor Klias Wild- 
man. The proportions are as follows: 

Pure silver 240 grains. 

" gold 24 " 

11 tin 17.5 « 

In preparing the alloy it should be melted and granu- 
lated four times to insure intimate admixture of the 
metals. It is afterwards placed in a flask and digested 
by the aid of gentle heat in chemically pure nitric acid 



GOLD. 277 

in the proportion of 2 parts acid to 1 of water. After the 
silver has all been dissolved the precipitate is allowed to 
settle, the supernatant liquid poured ofF and the precipi- 
tate washed several times with warm distilled water. It 
is then again subjected to the action of dilute nitric acid, 
aided by heat and continual stirring to dissolve any of 
the remaining silver. When all action subsides, pour the 
contents of the flask on a filter paper and wash all the 
nitrate of silver out with pure water. The filtrate should 
be frequently tested with sodium chloride. When the 
latter reagent will no longer throw down the white pre- 
cipitate of chloride of silver, the precipitated purple of 
Cassius on the filter paper is dried and is ready for use 
in the manufacture of gum frit. 

Purple of Cassius is very soluble in ammonia before 
fusion, after which it is insoluble. "That ignition," 
says Dr. Kirk, "does not effect such decomposition is 
proven by the fact that the ignited powder can have all 
of its gold extracted by aqua regia, leaving pure stannic 
oxide, or the gold may be extracted from it by amalga- 
mation with mercury, which is impossible before ignition. ' ' 

ALLOYS. — Gold very readily unites with most of the 
metals, forming alloys of varied qualities. When in the 
pure state gold is too soft for any great use other than for 
filling teeth; consequently the greater quantity of gold is 
alloyed with some metal that will increase its hardness 
and durability, without greatly impairing its more 
valuable qualities. The metals usually employed for this 
purpose are silver, platinum and copper. 

Silver and gold are easily mixed together, but do not 
seem to form definite compounds. Such alloys are more 
fusible, more ductile, harder, more sonorous and elastic 
than gold, and are generally of a greenish-white color. 
One-twentieth of silver is sufficient to modify the color 
of gold. The alloys of gold and silver are known to 



278 



PRACTICAL DENTAL METALLURGY. 



jewelers as yellow, green and pale gold, according to the 
content of silver. 

Copper and gold unite much more readily than silver 
and gold; indeed it is reasonable to believe from their 
behavior that a chemical combination is formed with 76 
per cent, of gold and 24 per cent, of copper. Alloys of 
copper and gold are much harder, tougher, and more 
easily fused; less malleable and ductile, and greatly 
changed in color, being of a decidedly reddish tint, de- 
pending upon the proportion of copper with which the 
gold is debased. An alloy of gold 76, and copper 24, as 
spoken of heretofore, is distinctly crystalline and quite 
brittle; but a larger proportion of either gold or copper 
restores the malleability of the alloy. 

Standard Gold. — The standard alloy of most nations 
is one of copper and gold. Some contain small quanti- 
ties of silver, but this is due to imperfect parting of silver 
and gold, or it may be contained in the copper used for 
the alloy. The proportion of copper to gold varies 
slightly in different countries, and such proportions are 
stated in thousandths; thus, pure gold is one thousand 
(1000) fine. The following table gives the composition 
of standard gold, as fixed by the nations mentioned: 



Nation. 


Gold. 


Copper. 


United States ") 


900 .... 




France 




Italy , 

Switzerland ' 

Spain 


100 


(Carat 
916 .... 


21.6—) 


Greece 

China 




Austrian Crowns 


84 


Ducats Hungarian 


989 .... 


11 


Ducats, Austrian 

Ducats, Dutch 


986 .... 


14 


982 


18 







GOLD. 



279 



The first United States gold coins were ten-dollar 
pieces, coined in 1795; they weighed 270 grains each, 
and were of 916.666 (22-carat) fineness. Their weight 
was reduced in 1834 to 258 grains, with 899.225 (21.581- 
carat) fineness; and in 1837 the present standard of 900 
(21.599-carat) fineness was established. 

Alloys of gold with copper, or with silver, or with 
both, are much used in the manufacture of jewelry. 
When the gold contains copper only it is termed red 
gold; when silver only, white gold; if the gold contains 
both metals, the caratation is termed mixed. In many 
countries a legal standard of fineness is fixed for gold 
ornaments and jewelry. In England gold is stamped, 
or Hall Marked, 16, 18, and 22-carat; in France, 18, 20, 
and 22-carat; in Germany, 8, 14, and 18-carat, and, 
also, under the term joujou gold, a 6-carat gold used for 
electro -plated jewelry. The purpose of the stamping is 
to protect the purchaser, who is enabled to know the 
carat of the gold he is buying. 

The following alloys used by jewelers are also of much 
interest to the dentist: 

TABLE OF MIXED CARATATION.— Brannt. 







Parts. 


carats. 


Gold. 


Silver. 


Copper. 


- 




... 23 .... 


23 


Vz .... 


Vz 






22 .... 


22 


1 


1 


... 






20 .... 


20 


2 


2 

3 






18 .... 


. . 18 . . 


3 






... 15 .... 


15 .. 


3 


.., 6 
.... 8 
8*4 






... 13 .... 


.... 13 .... 


3 






... 12 ... 
. . . 10 . 

9 .... 


.... 12 


3K .... 






.... 10 .... 
9 .... 


4 
W z 


... 10 
.... 10^ 






8 .... 


8 


h x A .... 


.... 10# 
9 






7 .... 


7 .... 


8 



















280 



PRACTICAL DENTAL METALLURGY. 





COLORED GOLDS.— Brannt. 




Parts. 


Color. 












Gold. 


Silver. 


Copper. 


Stee 


Cadmium. 




2 to 6 


1.0 








Green 


75.0 


16.6 






8.4 


«< 


74.6 


11.4 


9.7 




4.3 


<( 


75.0 


12.5 


• ♦ • • 




12.5 


(< 


1.0 


2.0 


• . • . 


• • • 


• • • ■ 


Pale yellow 


4.0 


3.0 


1.0 


■ • • i 




Dark yellow 


14.7 


7.0 


6.0 


• • • 




«< (i 


3.0 


1.0 


1.0 






Pale red 


10.0 


1.0 


4.0 


• ■ • 





<< (i 


1.0 




1.0 






Dark red 


30.0 


3.0 




2.( 


) 


Gray 


1 to 3 







l.( 


) 


Blue 



HIGHER CARAT COLORED GOLDS. 



Parts. 


Color. 


Carat. 


Gold. 


Silver. 


Copper. 


15 dwt 


2 dwt. 18 grs . 

1 " 18 " 

6 " 

2 " 


2 dwt. 6 grs.. 

3 " 6 " 
12 " 

5 " 

8 " 


Yellow tint 


18 K 


15 " 


Red " 


18 K 


1 oz. 16 dwt.. . 
1 oz 


Reddish Spring Gold. 
Yellow tint 


16 K 
16 K 


1 oz 


Red tint 


16 K 









Jewelers usually make their solders from the gold 
upon which they are to be used by the addition of 
small quantities of copper, silver or brass, the latter 
greatly increasing the fusibility and flow. The follow- 
ing are: 

jewelers' solders. 



For 18-Carat Gold. 
18-carat gold .... 1 dwt. 

Silver 2 grs. 

Copper 1 gr. 

Carat. — The fineness of 



For 16-Carat Gold. 

16-carat gold 1 dwt. 

Silver 10 grs. 

Copper 8 " 

gold is also expressed in 



carats, a twenty-fourth part, formerly the twenty-fourth 



GOLD. 



281 



part in weight of a gold marc. It is now assumed that 
there are 24 carats in unity; whether the unit be one 
pound, one ounce, or one pennyweight, it is divisible into 
24 equal parts, and each of these parts is called a carat 
to express fineness. If a quantity of gold is chemically 
pure, in other words contains no alloying elements, it is, 
as we have previously explained, 1000 fine; or, in other 
words, each 24th part is gold, and it is, therefore, said to 
be of 24-carat fineness. If, however, 2 carats, or 2-24ths 
of the unit quantity are composed of one or more alloying 
metals, the gold is said to be 22 carats fine; or if 6 carats 
or 6-24ths of the alloy is debasing metal, the carat is 18 
fine, etc. The following table shows the equivalent of 
each carat in thousandths: 



Carats. 


Thousandths. 


Carats 


Thousandths. 


... 1 ... 


.... 41.667 .... 


... 13 ... 


... 541.667 ... 




2 ... 


.... 83.334 








14 ... 


... 583.333 ... 




3 ... 


.... 125.001 








15 ... 


... 624.555 ... 




4 ... 


.... 166.667 




. 




16 ... 


... 666.667 ... 




5 ... 


.... 208.333 








17 ... 


... 707.333 ... 




6 ... 


.... 250.000 








18 ... 


... 750.000 ... 




7 ... 


.... 291 666 








19 ... 


... 79L.666 ... 




8 ... 


.... 333.333 








20 ... 


... 833.333 ... 




9 ... 


.... 374.999 




a 




21 ... 


... 874.999 ... 




10 ... 


.... 416.667 








22 ... 


... 916.666 ... 




11 ... 


.... 458.630 








23 ... 


... 958 333 ... 




12 


. 500.000 




• 




24 


1000.000 ... 



GOLD PLATE. — Pure gold is rarely employed in the 
dental laboratory, except for soldering continuous-gum 
cases and such. Its extreme softness and flexibility 
make alloying absolutely necessary. The latter must 
be accomplished, however, without practically impairing 
either its malleability, pliancy, or purity, and at the 
same time endow it with that degree of hardness, elas- 
ticity and strength necessary to resist the stress and wear 
which an artificial denture is exposed to in the mouth. 



282 



PRACTICAL DENTAL METALLURGY. 



Copper and silver are much used to debase or alloy, 
pure gold. It is questionable, however, whether copper 
should be used as almost universally as it is, some 
regard it as exceedingly objectionable. A plate made 
from a gold alloy containing a large percentage of copper 
is more easily tarnished, and imparts an ugly metallic 
taste, and may become a source of injury to the soft 
tissues of the mouth. 

Silver exercises a very benign influence over copper 
contained in gold plate, controlling the tendency to that 
disagreeable redness. Equal parts of silver and copper 
have little or no effect upon the color of gold. Silver 
assistsjin imparting hardness, elasticity and durability to 
the alloy, without so far debasing it as copper alone. 

Platinum and silver are sometimes used to endow 
pure gold with the qualities necessary for a dental base; 
but the labor of swaging is very greatly increased when 
platinum is contained in the plate. 

In order to secure the best results, alloys intended for 
plate should not be less than 20-carat fineness; 18 -carat 
is sometimes used; but in such cases the alloy should 
contain as little copper as possible. It is positively 
unsafe to use a lower carat than 18. 

The following are some of the formulae in use for the 
preparation of alloys for dental bases: 



Number 

of 
Formula. 


Carat. 


Parts Pure. 


Gold. 


Silver. 


Copper. 


Platinum, 


* 1 


18 
18 
18 
19 
19 
20 
21 
22 


18 dwts. 
18 " 

18 " 

19 " 

19 " 

20 " 

21 " 

22 " 


2 dwts. 

3 " 

4 " 

2 " 

3 " 
2 " 

1 dwt. 
18 grs. 


4 dwts, 
3 " 

1 dwt. 
3 dwts. 
Idwt. 

2 dwts, 
2 " 
Idwt. 




2 




3 
* 4 


Idwt. 


5 

* 6 

* 7 

* 8 


Idwt. 
6 grs. 



* Richardson's Mechanical Dentistry, p. 56. 



GOLD. 



283 



Number 




of 


Carat. 


Formula. 




t 9 


18 


* 10 


18 


X ii 


18 


* 12 

* 13 


19 
20 


X 14 


20 


* 15 

* 16 


21 
21 



Parts Pure. 



Gold. 



64y 2 dwts. 

($60 00) 
20 dwts. 
516 grs. 
($20 00) 
20 dwts. 
20 " 
516 grs. 
($20 00) 
20 dwts. 
20 " 



Silver. 



13 dwts. 

2 dwts. 

96.45 grs. 

(25 c. coin. 

40+grs. 

20 4- grs. 

10 c, coin. 

13 + grs. 



Copper. 



2 dwts. 



25 grs. 
18 " 



6 grs. 



Platinum. 



/ o-/ grs. 



CLASP GOLD. — Gold for clasps, elastic wires, back- 
ings, stays, posts, pivots, etc., usually contain a small 
amount of platinum to give it greater strength and elas- 
ticity. The following formulae are recommended by 
Professor Chapin A. Harris: 



No. 1— 20-Carat. 

Pure gold 20 dwts. 

" copper 2 " 

" silver 1 dwt. 

" platinum.. 1 " 



No. 2— 20-Carat. 

Coin gold 20 dwts. 

Pure copper 8 grs. 

" silver 10 " 

" platinum.. 20 " 



A content of platinum in gold renders the alloy more 
liable to oxidation, and, says Professor Harris, "This 
effect is so marked that such an alloy is readily acted 
upon by nitric acid." It is not probable, however, that 
the small amount contained in clasp gold would affect its 
integrity. 

CROWN GOLD.— Gold for crowns should combine 
strength with good color. Those alloys of a large copper 
content make exceedingly unsightly crowns, on account 
of their deep red color. Professor C. L. Goddard recom- 
mends the following for alloys the color of pure gold: 

♦Richardson's Mechanical Dentistry, p. 56. 

f Johnson Bros. 

X Prof. C. I,. Goddard. 



284 



PRACTICAL DENTAL METALLURGY. 



No. 1— 21.6-Carat. No. 2— 21.6-Carat. 

Pure gold 90 parts. Coin gold 50 parts. 

" silver 5 " Pure gold 45 l ' 

" copper... 5 " " silver 5 " 

GOLD SOLDERS.— These are usually alloys of gold, 
silver, copper aud zinc, and are designed to be a trifle 
more fusible than the parts to be soldered; this property 
is conferred upon them principally by the content of 
zinc (or brass). They should also possess considerable 
strength; too much base metal, therefore, should not be 
added, as it will, by oxidizing, tend to very materially 
weaken the alloys. Their carat should be as high or 
nearly as high as that of the plate, and color as nearly 
as possible the same. 

The following formulae have yielded satisfactory re- 
sults as gold solders: 



Parts. 





u 

o 


No. 


1 


14 


2 


14 


3 


15 


4 


16 


5 


16 + 


6 


18 


7 


18 


8 


20 


9 


20 


10 


14 



U.S. Coin 
Gold. 



$10.00 

16 dwts. 

6 " 



30 parts 
$10 00 



Pure 
Gold. 



Pure 
Silver. 



11 dwts. 

j 11 dwts ) 
112 grs. } 

27 parts. 



4 dwts. 



30 grs. 
3 dwts ) 
6 grs. . < 

3 dwts . 

4 parts. 
4 " 



5 dwts. 



f (18 K. gold plate 1 
J formula No. 9) 
1 20 dwts. 

(, Johnson Bros. 



12 grs. 



2.5 dwts. 



Pure 
Copper. 



Pure 
Zinc. 



118 
20 

\t 

I 1 
112 

1 



dwts. 
dwts ( 
grs. I 

grs. I 10 grs. 

dwts 
grs. 

dwt - I l<>ers 
grs. ) J - grb 1 

part. 1 part. 

parts. I t 1 " 



Spelter 
Solder.* 



6 grs. 



20 2TS. 



35 grs 



20.61 

grs. 

6 grs. 



A simple method for making a good solder suitable for 
the plate upon which it is to be used is : 5 parts of the 



* Composed of equal parts copper and zinc. 



gold. • 285 

plate and one of brass or of silver solder. In the case of 
coin gold, or the crown alloy given on page 284, a solder 
thus made will be exactly 18 carat.* 

Zinc is best added to the alloys in the form of brass. 
The latter should be of a known formula, so that the 
desired amount of zinc may be accurately calculated; it 
should also be malleable and ductile; or the solder is apt 
to be very brittle. 

RULES FOR COMPUTING AND COMPOUNDING 
GOLD ALLOYSf AND EXAMPLES J 

PART I. 
To ascertain the carat of any given alloy, the propor- 
tion may be expressed as follows: 

As the weight of the alloyed mass is to the weight of gold it 
contains, so is 24 to the standard sought. 
Example. — Gold 6 parts, silver 2 parts, copper 1 part, total, 9 

P arts - 9:6::24:? 

6 
9)144 

16 Answer. 

Another method when alloyed gold is used in forming 
the mass, instead of pure gold, is to express the propor- 
tion as follows — 

As the weight of the alloyed mass is to the weight of the gold 
alloy used in its composition, so is the carat of the latter to the 
carat of the former — 

Example. — Harris No. 1 solder: 

22-carat Gold 48 parts. 

Copper 16 " 

Silver 12 " 

Total 76 " 

76:48::22 carat. Ans. 13.9 carat. 

* Prof. C I,. Goddard. 

t Rules by Prof. Geo. Watt. 

X Examples by Prof. C. L,. Goddard. 



286 PRACTICAL DENTAL METALLURGY. 

EXAMPLES UNDER RULE 1ST. 

1. Find the carat of 36 pennyweights of gold, 8 pennyweights 
of copper, 4 pennyweights of silver. Ans. 18 carat. 

2. Find the carat of 9 pennyweights of gold, 2 pennyweights of 
copper, 1 pennyweight of silver. Ans. 18 carat. 

3. Find the carat of 38 pennyweights of gold, 6 pennyweights 
of copper, 4 pennyweights of silver. Ans. 19 carat. 

4. Find the carat of 22 pennyweights of gold, 1 pennyweight 
of copper, 18 grains of silver, 6 grains of platinum. Ans. 22 carat. 

5. Find the carat of 22 pennyweights of gold, 2 pennyweights 
of copper, 1 pennyweight of silver, 1 pennyweight of platinum. 

6. Find the carat of 6 pennyweights of gold, 2 pennyweights 
of copper, 1 pennyweight of silver. 

7. Find the carat of 48 parts of 22-carat gold, 16 parts of silver, 
12 parts of copper. Ans. 13.9 carat. 

8. Find the carat of 20 pennyweights of gold coin, 2 penny- 
weights of copper, 2 pennyweights of silver. Ans. 18 carat. 

9. Find the carat of 20 pennyweights of gold coin, 25 grains 
of copper, 40 + grains of silver. 

10. Find the carat of 20 pennyweights of gold coin, 18 grains 
of copper, 20 + grains of silver. 

11. Find the carat of 464.4 grains of gold, 5.16 grains of sil- 
ver, 46.44 grains of copper. 

PART II. 

To reduce pure gold to any required carat, the propor- 
tion may be expressed as follows: 

As the required carat is to 24, so is the weight of gold used to 
the weight of the alloyed mass when reduced. The weight of 
gold subtracted from this gives the quantity of alloy to be added. 

Example. — Reduce 6 ounces of pure gold to 16 carat, 16:24: :6 
ounces: 9 ounces. 9 — 6= 3 ounces alloy to be added. 

To reduce gold from a higher carat to a lower carat, 
the proportion may be expressed as follows: 

As the required carat is to the carat used so is the weight of the 
mass used to the weight of the alloyed mass when reduced. 

The weight of the mass used, subtracted from this, gives the 
quantity of alloy to be added. 



gold. 287 

Example. — Reduce 4 ounces of 20-carat gold to 1(3 carat : 

16:20::4 ounces:? 
4 

16)80 

5 ounces 

5 ounces — 4 ounces=l ounce alloy to be added. 

EXAMPLES UNDER RULE 2D. 

1. Reduce 6 ounces gold to 16 carat. Ans. Add 3 ounces alloy. 

2. Reduce 25 pennyweights gold to 18 carat. Ans. Add 8 
pennyweights, 8 grains alloy. 

3. Reduce 4 ounces of 20-carat gold to 16 carat. Ans. Add 1 
ounce alloy. 

4. Reduce 6 ounces of 18-carat gold to 15 carat. 

5. Reduce 15 pennyweights of gold coin to 20 carat. Ans. 
Add 1.2 pennyweights. 

6. Reduce 12 pennyweights of gold coin to 18 carat. 

7. Reduce 4 pennyweights of 22-carat gold to 20 carat. Ans. 
Add 9.6 grains alloy. 

8. Reduce 48 grains 20-carat gold to 16 carat. 

9. Reduce 2 pennyweights 20-carat gold to 18 carat. 

10. Reduce 1 pennyweight, 8 grains 18-carat gold to 16 carat. 

PART IIL 
To reduce gold from a lower to a higher carat, add 
pure gold or a finer alloy. 

As the alloy in the required carat is to the alloy in the given 
carat, so is the weight of the alloyed gold used to the weight of the 
reduced alloy required. 

The weight of the alloyed gold used subtracted from this gives 
the amount of pure gold to be added. 

Example. — Reduce 1 pennyweight of 16-carat gold to 18 carat. 
First subtract 16 and 18 from 24 to find the amount of alloy in 
each carat. 24 24 

JL8 _16 

6 : 8 :: 1 pennyweight:? 

I 

6)~~8 

l}i pennyweight. 

\]A, — 1=K pennyweight of pure gold to be added. 



288 PRACTICAL DENTAL METALLURGY. 



To reduce gold from a lower carat to a higher carat, 

by adding gold of a still higher carat. 

Subtract the lower carat and the required carat each from the 
highest carat (instead of from 24) and proceed as before. 

Example — Reduce 2 pennyweights of 16-carat gold to 18 carat, 
by adding 22-caret gold. 

First subtract 16 and 18 from 22. 

22 22 

18 16 

4 : 6:2 pennyweights : 3 pennyweights. 
3 — 2=1 pennyweight of 22-carat gold to be added. 

EXAMPLES UNDER RULE 3D. 

1. Reduce 1 pennyweight of 16-carat gold to 18 carat. Ans. 
Add 8 grains of gold. 

2. Reduce 2 ounces of 16-carat gold to 20 carat. Ans. Add 2 
ounces of gold. 

3. Reduce 11 pennyweights, 8 grains of 18-carat gold to 20 
carat. 

4. Reduce 9 pennyweights of 16-carat gold to 18 carat. Ans. 
Add 3 pennyweights of gold. 

5. Reduce 2 ounces of 20-carat gold to 22 carat. 

6. Reduce 18 pennyweights of 16-carat gold to 18 carat by add- 
ing 22-carat gold. Ans. Add 9 pennyweights of 22-carat gold. 

7. Reduce 3 pennyweights of 18-carat gold to 20 carat by add- 
ing gold coin. Ans. Add 3 pennyweights, 18 grains. 

8. Reduce 12 pennyweights, 10 grains of 16-carat gold to 20 
carat by adding gold coin. 

9. Reduce 20 grains of 16-carat gold to 18 carat by adding 
20-carat gold. 

MISCELLANEOUS EXAMPLES. 

1. Find the carat of 19 pennyweights of gold, 3 pennyweights 
of copper, 2 pennyweights of silver. Ans. 19 carat. 

2. Reduce 5 pennyweights, 4 grains of gold to 20 carat. 

3. Reduce 2 ounces, 4 pennyweights, 8 grains of 20-carat gold to 
18 carat. 

4. Reduce 12 pennyweights of 18-carat gold to 20 carat. Ans. 
Add 6 pennyweights of gold. 



GOLD. 289 

5. Find the carat of 20 parts of gold coin, 3 parts of copper, 3 
parts of silver (gold plate). 

6. Find the carat of 30 parts of gold coin, 1 part copper, 4 
parts of silver, 1 part of brass (solder). 

7. Reduce 258 grains of gold coin to 20-carat gold. 

8. Reduce 516 grains of gold coin to 18-carat gold. 

9. Reduce 4 pennyweights of 16-carat gold to 18 carat by 
adding gold coin. 

10. Reduce 3 pennyweights, 6 grains of 16-carat gold to 18 
carat by adding 20-carat gold. 

($10 gold coin weighs 258 grains — $0.10 silver coin, 38.58 grains.) 

11. Add 10 cents silver to $20 gold — find weight and carat. 

12. Add 25 cents silver to $20 gold — find weight and carat. 

{Gold coin, 20 pennyweights ] to formula for 
copper, 2 [- pure gold, and 

silver, 2 " ) find carat. 

{Gold coin, 20 pennyweights ) 

copper, 25 grains >■ do 

silver, 40+ " ) 

f Gold coin, 20 pennyweights) 

15. Change^ copper, 18 grains >• do 

[ silver, 20+ " ) 

{Gold, 18 pennyweights "J to formula for 
Copper, 4 [■ gold coin, and 

Silver, 2 " J find carat. 

17. A watchchain, 14 carats fine, weighs 2 ounces, 4 penny- 
weights, 16 grains. How much pure gold must be added to raise 
it to 20-carat gold ? 

18. A piece of jewelry, 12 carats fine, weighs 3 pennyweights. 
How much U. S. gold coin must be added to make it 18-carat 
fine ? 

19. Add 4 ounces, 16 pennyweights, 5 grains of 14-carat gold to 
2 ounces, 4 pennyweights, 16 grains of 16-carat gold and find the 
carat of the mixture. Ans. 7 ounces, 21 grains of 14.64-carat gold. 

20. How much pure gold must be added to the above mix- 
ture to make it 18 carat fine? 

21. How much U. S. silver coin and how much copper must be 
added to 3 ounces U. S. gold coin to reduce it to 18-carat gold 
containing equal parts of silver and copper? 



The alloys of gold and most of the metals have been 
discussed under the heads of the various metals. 



290 PRACTICAL DENTAL METALLURGY. 

TESTS FOR GOLD IN SOLUTION.— Sulphuretted 
Hydrogen or Ammonium Hydro-Sulphide throws 
down a brown precipitate of auric sulphide (Au 2 S 3 ). 
The second precipitant is not used, however, as the pre- 
cipitate is soluble in it, as it also is in the alkaline 
sulphides. Auric sulphide is insoluble in nitric or 
hydrochloric acid taken separately, but soluble in 
aqua regia. 

Ferrous Sulphate and Oxalic Acid precipitate the 
gold in the metallic state; it is a brown powder, darker 
in the instance of the former than the latter, but develops 
the color and luster of gold by being burnished with the 
finger-nail or instrument. 

Stannous and Stannic Chloride. — The most delicate 
test for gold is probably the formation of the purple of 
Cassius. 

EXPERIMENT No. 69.— To a weak solution of gold chloride (AuCl 3 ), 
add, drop by drop, a weak solution of the mixture of stannic and stannous 
chloride. An intense purple color results, which, without the solutions, have 
been largely diluted, or the resulting precipitate mixed with a large quantity 
of water; the color cannot be appreciated on account of its intensity. 

If the precipitate formed in the experiment above be 
dried and heated on charcoal a metallic globule results. 

Heat and Light. — Gold is reduced from many of its 
compounds by sunlight, and from all of them by more 
or less heat. 

ELECTRO-DEPOSITION OF GOLD— By Simple 
Immersion. — From an acid solution of gold chloride, 
the base metals, and silver, platinum, and palladium, 
deposit gold in the metallic state. In the double cyanide 
of gold and potassium, zinc will quickly become gilded, 
copper, brass, and German silver, slowly, and antimony, 
bismuth, tin, lead, iron, nickel, silver, gold, and platinum 
not at all. 



GOLD. 291 

Deposition by a Separate Current. — The Solu- 
tion. — There are many solutions prepared for electro- 
gilding, some being formed by chemical means, others by 
a separate current from the battery; but whether they 
are made by chemical or electrical process, the best for a 
thick reguline deposit is the pure double cyanide of gold 
and potassium. 

A cyanide solution may be prepared as follows : 

Dissolve 120 grains of pure gold in one ounce of 
chemically pure aqua regia, and thus preparing the 
chloride of gold, as described previously.* Dissolve the 
chloride obtained in 32 ounces of warm distilled water, 
and add to it 1^ ounces of magnesia; the gold is pre- 
cipitated. Filter and wash with pure distilled water, 
digest the precipitate in 10 parts of distilled water mixed 
with .75 part of nitric acid to remove magnesia; then 
wash the remaining oxide of gold with distilled water, 
until the wash-water exhibits no acid reaction with test- 
paper. Next dissolve 3 ounces of ferro-cyanide of 
potassium and 6 drams of caustic potash in 34 ounces 
of distilled water, add the oxide of gold prepared, and 
boil the solution about twenty minutes. When the gold 
is dissolved there remains a small amount of iron pre- 
cipitated, which may be removed by filtering the solu- 
tion. The liquid, a fine, clear, golden color, is then 
ready for use, to be employed either hot or cold, but a 
better and quicker deposit is nearly always obtained from 
the warm solution. 

In electro-plating objects the first essential is a fin- 
ished surface, which must be made just as it is desired 
to be when completed. The next is cleanliness. If it 
be a silver denture or any other metallic object it should 
first be cleaned of all surface combinations, as oxides, 

* Preparation of Chemically Pure Gold, p. 259. 



292 PRACTICAL DENTAL METALLURGY. 

sulphides, etc., by polishing in the ordinary way; then 
scrubbed with a solution of hot water and soap by means 
of a brass or steel scratch-brush on the lathe; then 
washed or boiled in a strong solution of caustic potash, 
afterwards washing in distilled water, and finally in an 
acidulated water to remove all traces of the alkali. 

When a sufficient coating has been formed the object 
is to be removed from the bath and burnished by the 
scratch brush or agate burnisher, moistened with a solu- 
tion of warm water and soap, until the surface is finished 
as desired. 

The apparatus is exceedingly meager and simple, con- 
sisting of a single cell and a glass bowl (preferably of 
perpendicular sides) to contain the solution. The latter 
may or may not be adjusted in a water-bath, according 
to whether the operator desires to work his solution hot 
or cold. Aside from these connecting and guiding wires, 
cathode and anode hooks, together with an anode, a 
thermometer, a scratch-brush, etc., are all that will be 
needed. 

EXPERIMENT No. 70.— A solution should be prepared by the students 
under the guidance of the instructor, and kept on hand for the practical use 
of the students in electro-gilding their " dummy work." 



CHAPTER XXI. 
AMALGAMS. 

An Amalgam is an alloy of two or more metals, one 
of which is mercury. 

The name is probably derived from the Greek malagma, 
meaning a soft material, and was applied to alloys of 
mercury on account of the increased plasticity and fusi- 
bility which it conferred upon them. 

Most metals, even hydrogen and ammonium, unite 
directly with mercury to form this very numerous and 
interesting series of alloys which are termed amalgams. 
Many are extensively used in the arts and industries; 
but to no art, calling, or profession can they be of more 
interest or importance than to dentistry. 

It must not be inferred that amalgams are to be given 
different chemical and physical theoretical consideration 
because they are studied thus distinctly. On the con- 
trary, they are to be considered in all respects alloys, 
differing from the usual in no general way, except that 
all contain mercury and are endowed with some proper- 
ties peculiar and dependent upon that metal. They 
are, therefore, subject to the same classification quoted 
from Matthiessen in the chapter on Alloys.* They offer 
an excellent opportunity for studying the behavior of 
metals towards each other, the examination being facili- 
tated by the low temperature at which their combinations 
are effected. f 

The affinities affording the union of mercury with its 
constituents in the formation of amalgams are not, as a 

♦The student should carefully review this elassi6eatiou. 
f Mercury, it must be remembered, is simply a metal fused at ordinary 
temperatures. 



294 PRACTICAL DENTAL METALLURGY. 

rale, strong, for many of them are decomposable by 
pressure, and all by considerable heat; yet, like all other 
metals, mercury tends to form definite chemical com- 
pounds with certain metals. The following have been 
formed by combining the metals named with mercury, 
and squeezing out the excess by means of hydraulic 
pressure to the amount of 60 tons to the square inch : 

Amalgam of lead, Pb 2 Hg.* 
" " silver, AgHg. 
i( " iron, FeHg. 
" " zinc, Zn 2 Hg. 

" copper, CuHg. 
" " platinum, PtHg 2 . 

Also " " gold, Au 4 Hg. 
" tin, Sn 2 Hg. 

A native compound of mercury and silver, known as 
Argnerite, Ag 6 Hg, is found crystallized in the form of 
the regular system. 

Beautiful crystallizations of silver amalgam (Arbor 
Diance) may be formed in long prisms having the com- 
position Ag 2 Hg 3 , by dissolving 400 grains of silver 
nitrate in 40 ounces of water, adding 160 minims of con- 
centrated nitric acid, and 1840 grains of mercury; in a 
few hours beautiful crystals of considerable length will 
be deposited. 

The union of mercury and other metals may be said to 
take place by four different means: 

(1st.) Some by direct co?itact, accompanied in some 
instances by a considerable evolution of heat. Thus, if 
a piece of clean sodium be thrown upon a clean, dry 
surface of warmed mercury, union takes place with 
explosiveness, accompanied by incandescence, and the 

* Bloxam's Chemistry, Inorganic and Organic, p. 400. 



AMALGAM S. 



295 



evolution of an amount of heat sufficient to volatilize 
portions of each metal. 

EXPERIMENT No. 71.— Repeat Experiment No. 8. 

(2d.) Some by the action of mercury on a salt of the 
metal, as the introduction of metallic mercury into a 
solution of a salt of the metal; and 

(3d.) Others by the action of the metal on a salt of 
mercury, as, the introduction of the metal into a solu- 
tion of a salt of mercury. 

EXPERIMENT No. 72.— Into a solution of mercuric chloride place a 
strip of clean aluminum. A deposition of mercury will take place on the surface 
of the aluminum. 

(4th.) By voltaic action, as when a metal is placed in 
contact with mercury in some acidulated solution. 

IN THE ARTS.— "Silvering."— The process known 
as "silvering on glass" was until recently a misnomer, 
as tin amalgam was alone employed in the manufacture 
of mirrors. This was accomplished on a perfectly 
smooth, flat, stone surface, surrounded by a wooden 
gutter. On this surface was smoothly spread a sheet of 
tin-foil somewhat larger than the glass to be operated on. 
A small quantity of mercury was rubbed over the surface 
of the tin to "quicken" the foil; the impurities were 
taken off, and mercury to the depth of about % of an 
inch, or sufficient to float the glass, was poured over the 
whole. The scum was then carefully removed from one 
end, and the glass, started there, was slid over the mer- 
cury-covered foil, carrying with it most of the superfluous 
mercury and the impurities; heavy weights were then 
placed upon the glass, until the greater part of the 
remaining mercury was pressed out. The table being 
tilted diagonally, all the superfluous mercury found its 
way to the gutter. After twenty-four hours the amalgam 



296 PRACTICAL DENTAL METALLURGY. 

backing was sufficiently hard and adherent for the glass 
to be moved aside for more perfect drying, which in 
the case of large sheets occupied some twenty-five to 
thirty days. 

"Fire-gilding." — Before the action of the galvanic 
current upon solutions of metals was understood, amal- 
gams were greatly used in the process known as fire- 
gilding or fire-silvering. This was effected by coating 
the object to be plated with the amalgam of the corre- 
sponding metal, and volatilizing the mercury by the 
application of heat, the gold or silver remaining as an 
adherent coat which was afterwards burnished into a 
compact film. 

The attraction of mercury for gold and silver is taken 
advantage of for the extraction of those metals from their 
ores. The addition of a little amalgam of sodium to 
mercury increases its combining power, and it more 
readily unites with other metals, even iron. This is 
especially recommended in the employment of mercury 
in the extraction of silver or gold from their ores. 

An amalgam of equal parts of tin and zinc with six 
parts of mercury is much used for rubbers on electrical 
machines. 

DENTAL-AMALGAM ALLOYS.— The term com- 
prehends those alloys composed principally of silver 
and tin, with the addition of small percentages of 
one or more other metals, which, when comminuted 
and mixed with mercury, form a coherent mass.* 

A DENTAL AMALGAM may, therefore, be under- 
stood to be a comminuted metal or dental- amalgam 

* Such a distinction precludes the confusion of the terms " Dental Alloy " 
and ' ' Dental Amalgam, the former of which we may understand as applicable 
to any of the numerous alloys used by dentists, for whatever purpose, and 
which do not contain, nor are designed to be mixed with, mercuiy; the latter 
being accepted as the Dental-Amalgam Alloy mixed with mercury. — Author. 



AMALGAMS. 297 



alloy mixed with sufficient mercury to form a cohe- 
rent mass. 

There are alloys which contain small percentages of 
mercury, added usually to lower their fusing points. 
Within the strict reading of the definition of amalgam 
these might be considered amalgams, but in the dental 
acceptation of the term they cannot be regarded as such. 

HISTORY.— "The introduction of amalgam," says 
Dr. Burchard,* " was not prompted by any specific merit 
that it had been demonstrated to possess, but was due 
solely to its properties of easy introduction, compari- 
tively perfect sealing and prompt hardening, qualities 
which apparently recommend its wide and general use to 
those not possessing the requisite degree of skill for the 
successful manipulation of gold foil." 

" Applied upon a bases of glaring empiricism, with 
an absence of technical skill, the material received the 
prompt and sustained condemnation which its abuse had 
warranted. The steps and phases of this opposition of 
the trained and skilled against untrained and unskilled 
operators may be read in the dental journals of from 1846 
to 1878, and even after. It was commonly known as the 
' amalgam war.' " 

Amalgam was probably first introduced in the year 
1826 by M. Traveau of Paris, who made an amalgam of 
pure silver and mercury and called it "Silver Paste." 
For convenience the pure silver was afterwards replaced 
by silver coin (composed of about 9 parts silver and 1 
of copper). This was introduced in America in 1833 
by the Crawcours, two French charlatans, under the 
name of "Royal Mineral Succedaneum." These adven- 

* Operative Dentistiy, Kirk, p. 219. 



298 PRACTICAL DENTAL METALLURGY. 

turers opened an office in New York and did a thriving, 
though unscrupulous, business for a time. This was the 
signal for the beginning of the heated opposition to this 
material already referred to. In 1841 the American 
Society of Dental Surgeons declared that any material 
containing mercury was injurious, and subsequently 
declared, its use malpractice. In 1845 this society 
exacted a pledge of its members not to use it. Many 
prominent members were using and advocating its use at 
the time, and the action on the part of the society met 
with such violent opposition that the requirement to sign 
a pledge was withdrawn. In 1849 Dr. Thomas Evans 
of Paris presented a formula of pure tin and cadmium. 
An amalgam made from this alloy was found to shrink 
and so greatly discolor the dentine of the teeth into 
which it had been introduced, that it was soon discarded 
by Dr. Evans himself. About this time Dr. Elisha 
Townsend of Philadelphia introduced his alloy of .silver 
42 and tin 58. The amalgam of this alloy received an 
immediate endorsement and application on account of 
the eminence of its author, but a reaction soon occurred 
which brought amalgams again under the ban. 

Soon after this time the " New-Departure Corps " was 
organized and espoused the cause of amalgams, and Dr. 
J. Foster Flagg made marked improvements in the silver- 
tin alloy. To his conscientious and faithful adherence 
to the use of plastics is due much of the credit for the 
present status of dental amalgams. 

The later investigations of Dr. G. V. Black have placed 
the study of amalgams upon a thoroughly scientific basis, 
and much may be expected from the work he has so 
scientifically begun. 



AMALGAMS. 299 



FORMATION OF DENTAL-AMALGAM AL- 
LOYS. — The directions for the preparation of alloys in 
general are equally applicable to the preparation of these 
special ones. The same precautions should be observed 
to avoid loss by oxidation, volatilization, etc. The 
manner of melting and pouring differs in no essential. 

It will, therefore, suffice to briefly illustrate the pro- 
cess by detailing the manner of preparing one from the 
metals usually employed, such as tin, silver, and gold or 
copper. 

The source of heat may be an open-grate coke or coal 
fire, the forge, or what is best adapted to the purpose, 
the small injector gas furnace devised by Mr. Fletcher 
for melting metals. The crucible may be the ordinary 
refractory sand or Hessian, a clay and plumbago, or the 
plumbago crucible alone, the latter being preferable after 
it has been tested by heat. The crucible selected should 
be placed in the furnace and heated to a bright red heat; 
then a sufficient quantity of borax should be added to 
properly cover the inner sides when the crucible is tipped 
and rotated with the tongs. 

The silver and gold or copper may now be added, 
preferably in small pieces of thinly rolled plate, and 
thoroughly heated until fused. Being sure that the 
borax is melted as thin as possible, the tin may be added 
in as large pieces as convenient, that they may readily 
sink and unite with the fused metals before oxidation can 
take place. The crucible should then be removed with 
tongs, the contents well shaken or stirred with a stick of 
soft wood, and quickly poured into the previously 
warmed and oiled ingot moulds, after which it is ready 
for comminution. 



300 PRACTICAL DENTAL METALLURGY. 

Borax is used as the flux, because it more perfectly 
protects the metals from oxidation and volatilization, ab- 
sorbing the oxides that may have been previously formed 
or developed during the fusing; protects the molten 
metals from the rough and porous sides of the crucible, 
and facilitates the pouring. 

The difficulty in adding tin is to avoid volatilizing any 
portion of it. It has been, therefore, melted separately, 
and the molten silver and gold or copper poured into it. 
This plan very thoroughly protects the tin, but it is ques- 
tionable if the less fusible metals are not so chilled that 
their proper alloying is prevented. In such a case the 
ingot should be broken up and remelted under plenty of 
borax. An exceedingly good plan to avoid volatiliza- 
tion is to wrap the volatile metal in soft paper that will 
conform readily to the sides of the piece of metal and 
quickly dash it beneath the surface of molten borax. 
The paper quickly chars and serves both as a covering 
and reducing material. 

The addition of zinc is probably the most difficult to 
accomplish without loss, as it so easily oxidizes. It is, 
therefore, sometimes united with a small amount of gold 
previously by wrapping the small grains of zinc in gold 
foil and thrusting them beneath the molten borax. 

Bismuth, antimony, and the other more fusible metals, 
are alloyed with the mass similarly to tin. Platinum, 
palladium, and such, with the silver, or silver and gold 
melted as recounted above. The appended table of Dr. 
J. O. Keller gives the composition of some of the prin- 
cipal dental-amalgam alloys in use:* 

* American System of Dentistry, Vol. Ill, p. 813. 



AMALGAMS. 



301 



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PRACTICAL DENTAL METALLURGY. 






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AMALGAMS. 303 



Liquation, or the separation of the constituents of 
the alloy, while molten or when being poured, on account 
of their differences in specific gravity and lack of affinity, 
may be best prevented by raising the alloy to a very high 
heat, stirring it with a stick of green wood, and pouring 
quickly. If it be suspected after pouring, the alloy should 
be remelted and again poured. Remelting is very apt to 
change the composition, and should be avoided where 
possible. 

COMMINUTION.— Alloys are generally comminuted 
or broken up into small particles by rasping or filing 
into grains, or turned into shavings on the lathe. 

An alloy rich in tin should be cut with a very coarse 
file, or, better, turned on the lathe, as it is frequently so 
soft that, clogging the file, it hinders further cutting. 
One rich in silver, however, presents a harder quality, 
and may be best comminuted with an ordinary coarse file. 

After the alloy has been comminuted it should be 
passed through a fine wire sieve to remove all coarse 
pieces, borax, bits of wood, leather from the wire file- 
brush, and other undesirable admixtures. After this the 
filings should have a magnet passed through them until 
no iron filings adhere to it; they should then be spread 
out over a broad surface and carefully and gently blown, 
either by the breath or small bellows, to remove any dust. 

A finely cut alloy takes up more mercury, contracts 
more, and is more plastic than a coarsely cut one, accord- 
ing to Dr. Black, who also says: "The cut in medium 
coarse filings — not so coarse as to seriously interfere with 
making a reasonably smooth mass — makes a much 
stronger amalgam, and one that contracts less with a 
given percentage of silver below 60 per cent, than if cut 
fine." 



304 PRACTICAL DENTAL METALLURGY. 

AGEING. — Freshly comminuted alloys have been 
found to undergo a change as regards their affinities and 
working properties after a time. Investigation tends to 
demonstrate that this change is more directly due to tem- 
perature than time. For example : a certain alloy may 
be freshly comminuted and an amalgam made of it immedi- 
ately, which upon examination is found not to shrink, 
but on the contrary may expand. The fresh comminu- 
tion may then be subjected to a slightly elevated temper- 
ature for a short time and an amalgam afterwards made 
of it which will be found to shrink. 

Dr. Black suggests the following explanation for the 
change: " In the cutting of an alloy the violence used 
hardens it, producing an allotropic condition of the 
metal, in which its chemical relations to mercury are 
profoundly changed. High temperatures, or even ordi- 
nary temperatures acting for a considerable time, have 
the effect of annealing the cut alloy and restoring its 
normal condition."* 

Freshly cut alloys may be artificially aged, according 
to Dr. Flagg, by placing the comminuted alloy in any 
convenient receptacle and subjecting it to the temperature 
of a boiling water-bath for ten or fifteen minutes. Dr. 
Black considers "low temperature ageing" superior: 
"The ageings at 110° [F.] and the ageings in the sun 
[95° to 105° F.] produce the best working property." 
The author has found that these low temperature age- 
ings require several days in the sun or forty-eight to 
sixty hours when the heat is continuous at 110° F. 

The student naturally inquires: Should all alloys be 
aged before using; or, how shall we determine which 
should and which should not ? Dr. J. Foster Flagg 

* Physical Properties of Silver-Tin Amalgams, Dental Cosmos, Vol. 
XXXVIII, p. 976. 



AMALGAMS. 305 



claims that ''there is no alloy made that does not work 
better results after it has been cut several weeks"; that 
those used freshly cut "shrink notably, set slowly, bulge 
markedly, and have little or no edge-strength." 

By exceptionally painstaking experiments and accurate 
deductions from them, Dr. Black furnishes us with a very 
scientific study of these changes. >:< Contrary to Dr. 
Flagg's views, he demonstrates that the value of ageing 
depends upon the formula of the alloy. For example, an 
alloy of silver 65 and tin 35, made into an amalgam, 
when freshly cuts/trunk not at all; but, instead, expanded 
one ten-thousandths of an inch. An amalgam made of 
the same alloy, after annealing shrunk ten ten-thou- 
sandths of an inch. On the other hand, an alloy con- 
sisting of silver 72.5 and tin 27.5 freshly cut and made 
into an amalgam expanded forty-two ten-thousandths 
of an inch, while the amalgam made of the same alloy 
annealed shrunk three ten-thousandths of an inch. As 
will be seen by the accompanying tables of Dr. Black's, 
annealing seems to decrease the expansion and increase 
the shrinkage. 

As a solution to the foregoing inquiry : If the operator 
prefers to use freshly cut alloy, the comminution should 
be followed immediately by amalgamation, and the 
amalgam thus made should be such as will neither shrink 
nor expand, or at least these changes should be as near 
zero as possible. On the other hand dealers and users 
of aged alloys must see to it that the alloy is of such a 
formula that age, either natural or artificial, brings these 
changes of expansion and contraction of the amalgams 
made from them down to a minimum. f 

*See tables, page 306. 

t The student should be directed to Dr. Black's article, Physical Properties 
of Silver-Tin Amalgams, Dental Cosmos, Vol. XXXVIII. p. 965. 



306 



PRACTICAL DENTAL METALLURGY. 



TABLE 


OF UNMODIFIED SILVER-TIN ALLOYS.* 


Formulae. 


How Prepared. 


Ph 


Shrinkage in 

Ten-Thousandths 

of an Inch. 


Expansion in 

Ten-Thousandths 

of an Inch. 


o 
<u 
&>•>' 

u 

<u 

Ph 


'M 


Silver. 


Tin. 


u 

a 
o 

Pm 


40 


60 

60 

55 

55 

50 

50 

45 

45 

40 

40 

35 

35 

30 

30 

27.5 

27.5 

25 

25 


Fresh-Cut 


45.78 
34.14 
49.52 
32.13 
51.18 
37.58 
51.62 
40.11 
52.00 
39.80 
52.00 
33.00 
55.00 
40.00 
55.00 
45.00 
55.00 
50.00 


6 

9 
4 

11 
2 

17 
2 

18 
1 

17 


10 

7 

3 




7 

3 
8 
1 
2 
1 
2 




1 


14 



42 


60 

6 


40.15 

44.60 

25.46 

28.57 

22.16 

2103 

19.66 

17.53 

9.06 

14.10 

3.67 

5.00 

3.45 

4.67 

3.92 

3.76 

5.64 

5.40 


178 


40 


Annealed 


186 


45 


Fresh-Cut 


188 


45 


Annealed 


222 


50 

50 


Fresh-Cut 

Annealed 


232 

245 


55 


Fresh-Cut 


245 


55 


Annealed 


276 


60 


Fresh-Cut 


239 


60 


Annealed 


297 


65 

65 


Fresh-Cut 

Annealed 


290 

335 


70 

70 


Fresh-Cut 

Annealed 


316 

375 


72.5 


Fresh-Cut 


275 


72 5 


Annealed 


362 


75 


Fresh-Cut 


258 


75 


Annealed 


300 









TABLE OF MODIFIED SILVER-TIN ALLOYS. 



Formulae. 



Modifying 
Metal. 



Gold 5 

Gold 5. . 
Platinum 5. .. 
Platinum 5. . 
Copper 5. . . 

Copper 5 

Zinc 5 

Zinc 5 

Bismuth 5 — 
Bismuth 5 . . 
Cadmium 5 ... 
CadmiumS. . 

Lead 5 

Lead 5 

Aiuminum5. . 
Aluminum 1. . 
Aluminum 1. 



Silver. 



65 

65 

66.75 

66.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

61.75 

6175 

61.75 

61.75 

61.75 

64.5 

64.5 



Tin. 



35 

35 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33.25 

33 25 

33.25 

33.25 

33.25 

33.25 

33.25 

34.5 

34.5 



How 
Prepared. 



Fresh-Cut. 

Annealed . 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Annealed. 
Fresh-Cut. 
Fresh Cut. 
Annealed. 





t/3 


in 






,d 


c £ 


<+-! 


■4-1 U 


V £ u 


s 3 a 




V u 
(J u 




Expansi 

en-Thous 

of an Ii 


u 


Pi 




V 

Ph 




£h 


H 




52.33 





1 


3.67 


33 00 


10 





5.00 


51.52 





4 


3.35 


33.53 


7 





5.06 


47.56 





1 


4.62 


30.35 


7 





6.07 


51.87 





9 


9.68 


37 33 


7 





8.20 


53.65 





23 


2.38 


35 60 


5 





3.50 


56.65 





68 


1.83 


40.65 





9 


2 07 


46.26 








4.78 


23.67 


6 





5.58 


57.57 





100 


6.40 


47.25 





5 


3.54 


44.17 





1 


4.88 


32.76 


10 





7.18 


65.00 





445 




46.98 





166 


12.60 


38.26 





48 


17.90 



bo 



T3 'Ji 



290 

335 
329 
380 
330 
395 
273 
352 
343 
416 
290 
345 
288 
308 
225 
290 
290 
276 

198 

213 



* See foot-note on opposite page. 



AMALGAMS. 307 



MERCURY. — The percentage of mercury required 
for the amalgamation of these different alloys varies 
greatly. If too much be added in mixing, the resulting 
solution becomes so liquid that it is worked with diffi- 
culty, if at all; if too little, the mass of alloy lacks co- 
herence and homogeneity, and the result of its attempted 
working is unsatisfactory. The mercury, of course, 
should be pure. Any admixture or cheminal combina- 
tion of a foreign substance necessarily serves to weaken 
the affinities of the mercury, resulting in less mass 
strength of the compounds developed or metallic solution 
made. 

There is no doubt amalgams are largely chemical 
compounds formed in definite chemical proportions 
with a mutual satisfaction of exacting affinities. The 
study of amalgamation; the solution formed when the 
alloy and mercury are brought into combination; the 
tendency to crystallization, accompanied by an evolution 
of more or less heat, and the peculiar, softly grating 
sound produced by compressing and rubbing the mix in 
the hand, sometimes called the "crepitus," resulting 
from the passing or rubbing of the crystalline particles 
over each other, and other phenomena, admit of no 
other conclusion. We are, then, to bear in mind still the 

^^^ y tilte^ The Wedelsteedt test-tubes, in which these 

^JK ^ fillings were inserted for examining them under 

/^^^^^ S^^ ^^^ft^ the microscope, and for other tests, are made of 

i^HHI KJMBjHBBiil hardened steel one-half-inch deep and one inch in 

jBSE ^S^=S wt -3Hlfj diameter, with a cavity three-eighths of an inch 

-llflk ' / : H : M-^ v'"^ ^-A ^ n diameter and one-fourth of an inch deep. The 

"fliHiR^ ■■"" -~ ; ~ ^iillMl ^ ace or to ^ °f tl ie tube is ground flat on a hone, and 

/ ^BKIiililif^ r= ^""''lIlP tne lnar K"i u of the cavity brought to a perfect 

'^^Bil ffi ft |j|jl|l||i ii! 1 ' ' :> /l^ilp* edge. They are so arranged as to place them on 

^ ;s Mli!||!|^ the stage of the microscope, and rotate them so 

I<ig. So. as J.Q bring ever}' part of the margin of the cavity 

under the lens in the same relation to the angle of the rays of light chosen 

for the examination. — Black. 

In the illustration the test-tube is empty. 



308 PRACTICAL DKNTAL METALLURGY. 

four conditions suggested by Matthiessen: "An alloy 
[or amalgam] may be either, (first) a solution of one 
metal in another; (second) a chemical combination; 
(third) a mechanical mixture; or, (fourth) a solution or 
mixture of two or all of the above. 

The increase of the silver component above 60, and 
especially above 65, per cent., requires a very nota- 
ble increase in the amount of mercury necessary. "With 
70 per cent, of silver," says Dr. Black, "it becomes 
very difficult to form a workable mass with 50 per cent. 
of mercury, while with 80 per cent, of silver it be- 
comes necessary to use as much as 60 per cent, of mer- 
cury. The disposition to expand becomes notable in 
connection with this increase in the amount of mercury 
required. An increase in the amount of mercury 
required is also noted in descending the scale of the per- 
centage of silver in the range below 60 per cent., though 
this increase is less marked. It seems from careful ob- 
servation on this point that a good working mass can be 
made with less mercury at about 60 per cent, of silver 
than with any other proportion." 

Aged alloys require a less percentage of mercury 
than the freshly cut of the same formula. An excess of 
uncombined mercury over a certain percentage weakens 
the mass. 

AMALGAMATION. — The union of one or more 
metals or an alloy with mercury. 

This is accomplished usually by adding the mercury 
in excess to the comminuted alloy in the palm of the 
hand, mixing and kneading it into a pliant mass, and 
wringing out the excess through muslin or chamois skin 
by means of heavy pliers. 

Some prefer to add the mercury in excess to the com- 
minuted alloy in a wedgewood or ground-glass mortar 



AMALGAMS. 309 



directly, or, after mixing in the hand, then kneading into 
a pliant mass in the mortar and squeezing out the excess 
of mercury as before. 

Again, a great deal of pains is often taken to accu- 
rately determine the amount of mercury necessary for a 
given alloy or formula, and that determined amount is 
accurately weighed out and added for each separate mix. 

A variety of instruments and apparatus have been in- 
troduced for weighing, mixing, and what not, but it is 
probable that most practitioners adhere to the method of 
mixing in the hand, as first described. It may be urged 
that such a method is empirical and unscientific, but 
such is not the case. On the other hand, it appears to 
the writer as most impracticable to endeavor to calculate 
the exact amount of mercury necessary to combine a 
comminuted alloy of given formula into a coherent mass. 
The influences which increase or diminish the required 
amount are too numerous and difficult to anticipate. For 
instance: The affinity of metals acting separately with 
mercury is one thing, while the affinity of the same metals 
combined and then united with mercury is entirely 
another. It is improbable that two melts of the same 
alloy will be exactly alike, and quite possible that two 
portions of the same ingot carry a different formula. The 
manner of comminuting is not always the same; a great 
difference in the amount necessary for finely and for 
coarsely comminuted alloy is observed; age of the alloy 
has a very marked effect, as does the manner of mixing 
and manipulation. 

But if the mercury be added to the alloy in excess, and 
the affinity of the compound, mixture, or solution be 
satisfied, demonstrating its satisfaction by crystallization, 
and the excess filtered out, it seems to the writer just as 



310 PRACTICAL DENTAL METALLURGY. 

scientific as the crystallization of any salt from its solu- 
tion by the process of filtration and evaporation. 

It is particularly important in the mixing and working 
of an amalgam that the mercury be evenly distributed 
throughout the mass, and that all violence, such as grind- 
ing in a mortar or squeezing in a vise, be avoided, as it 
tends to weaken the amalgam. Dr. Black says, ' ' Grind- 
ing in a mortar causes an alloy to take up more mercury 
than when mixed in the hand or in a rubber mortar, but 
even when given the same percentage of mercury the 
product is weaker." 

EXPANSION AND CONTRACTION. —The co- 
efficient of expansion or contraction cannot be dem- 
onstrated as constant for the same amalgam, for the fact 
that it is quite improbable that two ingots of an alloy can 
be made alike; that each mix will contain the same 
amount of mercury; or that all will be cut, mixed or 
manipulated the same. 

Some amalgams both shrink and expand. The 
shrinkage occurring as the first and more rapid move- 
ment and expansion following slowly for several days. 
This dual movement is greatest in amalgams made from 
the silver 40 and tin 60 alloy,* diminishing with the in- 
crease of silver, and is seldom seen after passing a 60 per 
cent, content of that metal. Ageing or annealing the 
cut alloy increases the shrinkage and decreases the ex- 
pansion following it. 

Expansion. — Silver seems to influence expansion 
greatly we find as we study Dr. Black's experiments. 
An alloy of silver 65 and tin 35, freshly cut, amal- 
gamated, and packed in a Wedelstaedt test-tube, f 
expands .0001 of an inch after setting. This ten- 

* See table, p. 306. 

f See p. 307, for description of this test-tube. 



AMALGAMS. 311 



dency to expand rapidly increases as the content 
of silver is increased; when at the point of silver 
75, and tin 25 amalgams made of the freshly cut 
alloy expand .0060. Annealing brings the first (silver 
65, tin 35,) down to .0010 contraction, and the last (silver 
75, tin 25,) to only }{ of the original expansion, viz., 
.0006 of an inch. 

A content of 5 per cent, platinum* seems to somewhat 
increase expansion, copper more so, zinc still more, 
cadmium still greater, and aluminum very greatly. 
Aluminum 5, silver 61.75, tin 33.25, forms an alloy which, 
when amalgamated, expands .0445. These expansions 
are all greatly reduced by annealing. The greatest 
expansion found in amalgams made from fresh-cut 
alloys used as filling material is in one composed of 
silver 75, tin 20, and copper 5, which expanded .0123- 
The appearance of an expanded amalgam is similar to 
that of ice at the mouth of an iron tube in which water 
has been frozen. 

Contraction. — Tin has been said to influence a 
contraction in amalgam. Considering Dr. Black's experi- 
ments on silver-tin amal- 

gams we find the greatest 
contraction in amalgams 
made from the freshly cut 
alloy is obtained from the 
silver 40, tin 60 alloy 
(.0006). This change rep- 
resents its first movement, 
however, and is followed IG * 

by an expansion of .0007, leaving the amalgam finally 
expanded .0001 of an inch. This is altered by annealing 
to a primary contraction of .0009, followed by an expan- 

* See table of Modified Alloys, p. 306. 



r* ■ — 


/ 




/ 




i 


* 


i 


• 


i 




t 


i 


i 


■ 


4 


* 


1 

1 







312 PRACTICAL DENTAL METALLURGY. 

sion of .0003, leaving a final contraction of .0006 of an 
inch. In contraction the mass tends to assume the form 
shown in Fig. 36: 

The greatest shrinkage in an amalgam used as a filling 
material is found in that made from silver 54.86, tin 
48.89, and zinc .25, which reached .0020 of an inch. 

The greatest shrinkage in annealed alloys occurs from 
the alloy, silver 55 and tin 45, when the ultimate con- 
traction is marked at .0018. 

Strangely enough 5 per cent, content of bismuth or 
lead increases the contraction when added to silver-tin 
alloys. 

Copper amalgam is the only amalgam tested by Dr. 
Black which underwent no change of form in hardening, 
or setting. 

SPHEROIDING OF AMALGAMS.— It is reasonably 
held by most experimenters and writers that the com- 
position, methods of mixing, and handling of some amal- 
gams tend to promote an inherent disposition to assume 
a spheroidal or globular form on perfectly hardening. 
This, it is claimed, is manifested in the fillings made of 
these alloys, in that they raise out of and draw away from 
the sides of the cavity. No doubt much of this apparent 
elevation is, in reality, due to slovenly work, extending the 
filling material over the margins of the cavity and build- 
ing it fuller than necessary; subsequently a lack of edge- 
strength in the amalgam permits the portions so extended 
to be broken off, giving the plug the appearance of hav- 
ing been raised from its cavity. 

Dr. Black ascribes it to the expansion and flow of the 
mass; it being confined, has a tendency to rise up in the 
center, assuming a spheroidal form, much as ice does 
when forming in a glass, due to the flow produced by 



AMALGAMS. 313 



the stress caused from the expansion of the ice against 
the unyielding sides of the vessel. 

The cause of the spheroidal tendency has commonly 
been ascribed to the influence of tin; but of all the differ- 
ent amalgams tested by Dr. Black he found but two in 
the number which spheroided. Their formulae are as 
follows, and were made from freshly cut alloy. 

1. 2. 

Silver 80 Silver 75 

Tin 20 Tin 20 

Mercury 60 per cent. Copper 5 

Mercury ... 56. 56 per cent. 

No. 1. "Margins much raised with spherical surface sphe- 
roided, 11.1." 

No. 2. "Spheroided. 12.3." 

From such results we might conclude that the sphe- 
roidal tendency is caused by the excess of silver or mer- 
cury, or both; but such a conclusion cannot be safely 
drawn, nor is the problem one easy of solution, since 
it unquestionably involves the chemical affinities brought 
into play under these conditions. 

RESISTANCE TO STRESS.*— A silver-tin amal- 
gam, when fully hardened, presents a hard, brittle, 
metallic appearance. Its brittleness is such that when 
subjected to stress or pressure greater than its endurance, 

*Note- Of stress, Dr. Black, in the July, 1895, number of the Dental Cos- 
mos, p. 554, says: " The stress in the ordinary use of the teeth has been shown 
to be from sixty to eighty pounds upon the area of two molars of medium 
size. This, if evenly distributed, would give from seven and a half to ten 
pounds on a filling occupying one-fourth the area of one of these teeth. 
This would be a filling of ordinary size; but it frequently happens that the 
filling must bear all of this stress, and occasionally such fillings must bear 
all of the stress that the person is capable of exerting. Therefore, while the 
filling itself may not have to endure a stress of more than seven and a half 
to ten pounds in chewing a piece of beefsteak, it is continually liable to have 
to bear the whole stress when some hard substance is caught upon it, or even 
the whole stress the person can exert. This may be anywhere from one to 
two hundred pounds, or even a greater stress in some cases." 



314 PRACTICAL DKNTAI, METALLURGY. 



it goes to pieces suddenly with a crash like glass. It has, 
therefore, been commonly supposed that amalgam is 
brittle, and consequently exhibits no other change under 
stress. Such conclusions are but natural, since no metal 
or other alloy exhibits these seemingly incompatible 
properties of brittleness and ductility at the same time. 
Iron is malleable and ductile, as is soft steel, but hardened 
steel and cast iron are exceedingly brittle. Neither iron 
nor any of its compounds could be possessed of both of 
these properties at the same time. Yet Dr. Black's ex- 
periments tend to show, as he says, that "in this par- 
ticular the silver-tin amalgams seem to be an anomaly 
among the metallic compounds, for they are at the same 
time both very brittle and very ductile. If struck with a 
hammer they fly to pieces; but if subjected to a compara- 
tively light stress, either continuous or intermitting, 
they may be drawn out into thin laminae or molded into 
any form without breakage."* 

The resistance to stress in silver-tin amalgams made 
from freshly cut alloys increases very materially from the 
proportion of silver 40 and tin 60 which will withstand 
a stress of 178 pounds only, to that of silver 70 and tin 
30, which withstands a stress of 316 pounds without 
breach of continuity. After this an increase of silver 
causes a decrease in resistance to stress. Amalgam 
made from annealed alloys shows a somewhat higher 
crushing strength, but these, like those made from freshly 
cut alloys, show a decrease of crushing strength after 70 
percentage of silver is passed. Five per cent, of copper 
seems to increase the property of resisting stress more 
than any of the modifying metals used.f 

*Dr. G. V. Black, Filling-materials, Dental Cosmos, Vol. XXXVII, p. 556. 
fSee tables, p. 306. 



AMALGAMS. 315 



FLOW. — The property which causes a substance to 
continue to yield under a stress without breach of contin- 
uity as long as the stress is maintained. 

11 The standard being sixty pounds for one hour on a 
cube 85x85x85 thousandths of an inch, * * * a 
pure silver-tin alloy may be said to flow from two and 
a half per cent, to ten per cent., the difference depending 
on the composition of the alloy, the fineness of the cut, 
and the special mode of handling."* 

Dr. Black, in explaining this property of amalgams, 
says: " When the flow has begun it continues as long as 
the stress is maintained. No increase of stress is required 
to maintain the flow"; that " it will go slowly with a light 
stress, somewhat quicker with a heavy stress, but it can- 
not be made to go very quickly with a very heavy stress; 
it will break into fragments. A silver-tin amalgam is 
not malleable, "f His conclusions, based upon further 
experiments with silver and tin separately, are, that this 
property cannot be imparted by either of these metals, 
but results from the combination of the three — silver, 
tin, and mercury; and further, J " that the strength of 
the mass depends mostly on the perfect evenness of the dis- 
tribution of the mercury. Any irregularity in the work 
which disturbs this increases the flow," and after even 
distribution, ' 'any form of violence weakens the product." 
Finely comminuted alloys flow more than coarsely divided 
ones. 

The formula of the alloy largely controls the flow of 
the amalgam, and is of vastly more importance than the 
percentage of mercury or the manner of manipulation, 
provided both of these be reasonable. 

* Black, Filling-materials, Dental Cosmos, Vol. XXXVII, p. 5C6. 
f Ibid., p. 558. 
% Ibid., p. 561. 



316 PRACTICAL DKNTAL METALLURGY. 

It will be noticed in alloys having a large content of 
tin that the percentage of flow is greatest.* For ex- 
ample, an amalgam made of the fresh-cut alloy silver 40, 
and tin 60, under the standard pressure of 60 pounds for 
one hour, flowed 40.15 per cent. Ageing the cut alloy 
seems to generally increase the flow of amalgams made 
from it. Thus, in the formula given above (silver 40, 
tin 60, annealed), the flow was 44.60 per cent. As a 
rule the annealed alloy makes a softer and tougher 
amalgam. 

It will also be noted, by the tables, that the resistance 
to flow increases with the addition of silver, and that 
there is a notable increase in the resistance at sixty-five 
per cent., or, when we enter the group of hard alloys. 

"The crushing strength," says Dr. Black, "proves to 
be no test for the stability of an amalgam." All rea- 
sonable dental-amalgam alloys, when mixed with a 
" sufficiently low percentage" of mercury, are strong 
enough to withstand the stress of mastication. The 
flow, however, is an important test. The chief difficulty 
is, that while most of the alloys are capable of resisting 
the stress imposed, many of them will gradually change 
form under the same strain; thus, the appearance of the 
"black ditch " which is so often seen along the margin. 

The chief influences which disturb the maintenance of 
size and form of an amalgam filling are contraction or 
expansion, and flow; therefore a minimum of these 
changes are the primary considerations in a satisfactory 
dental amalgam. 

EDGE STRENGTH in an amalgam is the degree of 
resistance an edge or angle of an amalgam mass offers to 
force which tends to fracture it. 

* See tables, p. 306. 



AMALGAMS. 317 



1 'Amalgams have heretofore been regarded as rigid 
crystalline masses, utterly devoid of malleability. The 
discovery of the existence of flow at once modifies all 
previous conceptions and data regarding edge strength, 
for it is evident that a corner or angle might not fracture 
and yet flow under the stress of the impact of mastication, 
whereupon edge strength might be said to be great, and 
in reality be but slight. In view of the existence of the 
property of flow, edge strength must be measured as 
rigidity, the antithesis of flow, and a high crushing 
stress."* 

DISCOLORATION.— The discoloration of amalgam 
fillings is for the most part due to the action of sulphur- 
etted hydrogen. Silver and copper are readily attacked 
by this gas, forming the black, insoluble sulphides of 
silver and copper. Amalgams containing a larger pro- 
portion of either are blackened from this cause, nor will 
those metals (such as gold or platinum) which are them- 
selves untarnished by this agency, secure the same im- 
munity to amalgams containing them. The sulphide of 
cadmium is lemon-yellow; hence amalgams containing 
this metal are discolored (as is the tooth structure) a light 
yellow. 

CONDUCTIVITY.— As a conductor of thermal in- 
fluence, says Dr. Burchard,f amalgam is midway between 
gold and the basic zinc cements. 

WASHING. — Dental amalgams are frequently washed 
in alcohol, ether, or chloroform to remove oxides and 
oily matter attracted from the hand. It is, however, 
doubtful if such procedure gives any beneficial result. 
It has, however, been claimed that washed amalgams 
retain their color better. 

* Burchard. The American Text-Book of Operative Dentistry, p. 224. 
fThe American Text-Book of Operative Dentistry, p. 226. 



CHAPTER XXII. 
CLASSIFIED AMALGAMS. 

Dental-amalgam alloys may be classified as BI- 
NARY, TERNARY, QUATERNARY, QUINARY, 
Etc., according to the number of elementary constit- 
uents. 

A BINARY DENTAL AMALGAM may be com- 
posed of mercury alloyed with any ONE of the 
various metals used as constituents of dental-amal- 
gam alloys or dental amalgams, such as silver, tin, 
gold, copper, platinum, zinc, palladium, cadmium, 
bismuth, or antimony. COPPER and PALLADIUM, 
however, are the only ones which have thus far 
found any place of apparent usefulness. 

SILVER formed the prototype of binary dental amal- 
gams, as it did of dental amalgams in general. 

When finely divided, such as the precipitate, it readily 
and rapidly combines with mercury, evolving consider- 
able heat, and forming a hard mass in a few seconds. In 
the state of larger particles, such as filings, it combines 
more slowly. According to Mr. Fletcher,* "The rapid- 
ity of combination is reduced by the use of a mixture of 
precipitated silver and filings. If the precipitate is in 
excess, and the mass is inserted before the hardening 
commences, there is a risk of bursting the tooth by the 
gradual expansion of the mass — [which Mr. Kirby claims 
amounts to l-40th of the diameter of the plug] if a 
great excess of mercury is used the mass only partially 
hardens and the results are uncertain." 

Silver is, however, the most important and essential 
component of dental-amalgam alloys, and is usually the 

* Dental Metallurgy, p. 33. 



CLASSIFIED AMALGAMS. 



319 



largest component of their composition. It unites chem- 
ically with mercury to form definite chemical compounds* 
having the varying formulae of Ag 6 Hg, Ag 2 Hg 3 , and 
AgHg. It is readily discolored by sulphur compounds. 
TIN very readily combines with mercury, forming a 
friable, very slowly and imperfectly hardening amalgam. 
It is very probable that the action of tin and mercury 
when combined is a decided contradioji of the mass. It 
has been stated by some that the mass expanded, and by 
others that it contracted, but acurate data are wanting. 
The author bases his opinion entirely upon the data fur- 
nished by Dr. G. V. Black. f In arriving at this con- 
clusion, however, it is necessary to eliminate so many 
factors of influence, such as chemical affinities, fineness 
of cut of the alloy, manner of mix, manipulation, etc., 
that the opinion after all may seem of little value. The 
following notes of Dr. Black, rearranged, formed the data: 





Formulae. 






Fillings, 
how 


Fresh-cut. 


Per 

cent 

of 
Mer- 


How 
Mixed. 


Inserted 








Silver. 


Tin. 


cury, 




Hand pressure 

K It 


70 
65 


30 
35 


46.36 
44.6 


Hand . 

(i 


II (1 


60 


40 


37.85 


(< 


(I (1 


42.45 


57,55 


37.27 


<< 


Burnished .... 


42.45 


57.55 


45.31 


Mortar 



Contraction = ( — 

Expansion = (+) 

Unit of 

Measurement 

1 Thousandth 

of an inch 



+ .1.-.1 
Neither 
.05, -f .1, —.05 
.8, +.2, -.2 
,9, +.1 



Amount of 

Contraction or 

Expansion 

if any. 



Equalized 

Neutral 

Equalized 
— .0008 maximum 
— .0008 



Tin and mercury show a disposition to unite — forming 
a definite chemical compound of a weak crystalline 
nature said to have the formula Sn 2 Hg. It is second 
to silver in importance as a constituent of dental-amalgam 
alloys. 

* See p. 294. 

t Contraction and Expansion of Silver-Tin Amalgams, Dental Cosmos, 
Vol. XXXVII, p. 648. 



320 PRACTICAL DENTAL METALLURGY. 

v GOLD combines with mercury at any temperature, but 
more readily if either or both be heated slightly. Finely 
divided it combines even more rapidly. " Gmelin states 
that an amalgam of 6 of mercury to 1 of gold crystallizes 
in four-sided prisms, and that the mercury may be dis- 
tilled off from this leaving the gold in the arborescent 
form."* 

COPPER possesses the property of combining with 
mercury to form an amalgam which, on hardening or 
setting, may be softened by heat, kneaded, and inserted 
as a filling, and again becoming hard may be polished. 
It retains its metallic luster for some time when exposed 
to air, but blackens quickly when in contact with air or 
moisture containing sulphuretted hydrogen. Its peculiar 
properties have led to its introduction as a dental amal- 
gam, first known as Sullivan 's Amalgam or Cement. Its 
preparation and properties Mr. Fletcher describes as fol- 
lows:! " Precipitate from a weak solution of sulphate of 
copper by rods of pure zinc. Wash the precipitated cop- 
per with strong sulphuric acid (the addition of a small 
quantity of nitrate of mercury assists greatly), and add 
mercury in the proportion of 3 copper to 6 or 7 mercury. 
This alloy has the property of softening with heat and 
again hardening after a few hours." 

This amalgam has been thoroughly tried as a dental 
filling-material, and its use practically discontinued on 
account of the intense blue-black discoloration of its sur- 
face and the teeth containing it, and its undeniable surface 
disintegration. It has been thought to possess thera- 
peutic value; indeed, Dr. Kirk says: " Its preservative 
qualities render it a valuble constituent in alloys for use 
in teeth of a low grade of structure." Of it Dr. Black 

*Makins' Metallurgy, p. 268. 
f Dental Metallurgy, p. 60. 



CLASSIFIED AMALGAMS. 321 

says.* " This amalgam has so many good qualities that 
many abandon it with much regret. I think it generally 
acknowledged that copper amalgam fillings retain good 
margins, when they are once made good, better or more 
perfectly than any other filling-material." He shows 
that frequent reheating deteriorates the amalgam very 
materially; claims that it will not flow under stress and 
<( within the limits of its strength it is as rigid as 
hardened steel"; that it does not contract, but exhibits 
very slight expansion on setting, and attributes the 
properties heretofore assigned to its therapeutic qualities 
to the fact that it simply more perfectly seals the cavity. 

A variety of methods of preparing copper amalgam 
has been taught in the classrooms and described in our 
literature, some of which are as follows: 

Dr. T. H. Chandler's method for making his " No.l " 
and " No. 2 " is as follows :f 

No. 1. To a hot solution of sulphate of copper add a 
little hydrochloric acid, and a few sticks of zinc, and 
boil for about a minute. The copper will be precipitated 
in a spongy mass. Take out zinc, pour off liquor, and 
wash the copper thoroughly with hot water. Pour on 
the mass a little dilute nitrate of mercury, which will 
instantly cover every particle of the copper with a coat- 
ing of the mercury. Add mercury 2 or 3 times the 
weight of the copper, triturate slightly in a mortar, and 
finish by heating the mixture a few moments in a crucible. 

No. 2. Take finely divided copper (copper dust) 
obtained by shaking a solution of sulphate of copper 
with granulated tin; the solution becomes hot, and a fine 
brown powder is thrown down. Of this powder take 
20, 30, or 36 parts by weight and mix in a mortar with 
sulphuric acid, 1.85 specific gravity, to a paste, and add 
70 parts of mercury, with constant stirring. When well 
mixed wash out all traces of acid and cool off. When 

* Copper Amalgam, Dental Cosmos, Vol. XXXVII, p. 737. 
f Dental Chemistry and Metallurgy, Mitchell, p. 141. 



322 PRACTICAL DENTAL METALLURGY. 

used heat to 1300° F. It can be kneaded like wax in 
a mortar. (See Dr. Kirk's method of preparing copper 
amalgam, p. 209.) 

PLATINUM.— " Worked platinum," says Mr. Ma- 
kins,* " cannot be amalgamated with mercury, and the 
only method of forming platinum amalgam consists in 
rubbing finely divided platinum (such as that reduced 
from the ammonio-chloride) and mercury together in a 
warm mortar; the combination of the two will be accel- 
erated by moistening the two metals with water, acidu- 
lated with acetic acid, "f 

ZINC readily amalgamates with mercury to form a 
very brittle amalgam, whatever may be the relative pro- 
portion. With large amounts of mercury it forms an 
amalgam similar to that of copper, but too brittle for 
dental use. Zinc plates used in batteries are amalga- 
mated best by heating to about 482° to 500° F., and after 
quickly and uniformly coating them with a solution of 
the chloride of zinc and ammonia, dipping them at once 
into mercury. Amalgamation takes place immediately, 
and plates so amalgamated give currents of greater con- 
stancy and intensity than the ordinary zinc plates. Since 
the amalgam of zinc is not acted upon by dilute sul- 
phuric -acid, there is no wasting while the battery is not 
in use, the zinc being dissolved only while the circuit 
is closed. 

PALLADIUM may be precipitated from its solution 
by metallic iron or zinc. It should then be washed with 
weak nitric acid, and dried. This character combines 
quite readily with mercury, attended by evolution of 
heat. It hardens quickly as it cools, but may be com- 
bined so as to set quickly or slowly, depending upon the 

* Metallurgy, p. 304. 

f See chapter on Copper. 



CLASSIFIED AMALGAMS. 323 

proportion of its constituents. It turns very dark, but 
does not greatly discolor the tooth structure. On account 
of its quickly setting property it is difficult to work, and 
if inserted imperfectly it may harden so soon that it is 
almost impossible to remove it. Tombes says it shrinks 
less than any of the binary amalgams. The expensive- 
ness of palladium has caused the use of this amalgam to 
be almost, if not entirely, discontinued. 

Mr. Fletcher says:* 

" It may be prepared to combine with mercury so as to 
set quickly or slowly by varying the strength of the solu- 
tion; but it must be borne in mind that unless precipitated 
palladium sets very rapidly when mixed with mercury, 
it is totally useless for dental purposes; the plugs fail, 
unless fully hard, in so short a time, that the amalgam 
is difficult to insert whilst it remains plastic. Plugs of 
palladium amalgam generally contain about 70 to 80 per 
cent, of mercury. "f 

CADMIUM forms a silver-white, somewhat brittle 
amalgam of a crystallo-granular texture, which under 
certain circumstances is said to be malleable, imparting 
that quality to its alloys. 

ANTIMONY AND BISMUTH.— (See chapters on 
these subjects.) 

* Dental Metallurgy, Fletcher, p. 41. 

f Note. — Mr. Coleman in the subjoined gives his preparation of palladium 
amalgam: "About as much mercury as -would fill the cavity to be treated is 
placed in the palm of the hand, and the palladium powder very gradually 
added. It requires some careful rubbing with the forefinger before the two 
become incorporated, when it should be divided into smallish pellets, and 
these rapidly carried one after another to the cavity, each piece being well 
compressed and rubbed into the inequalities of its walls by a burnishing or 
compressing instrument and with a rotary movement of the hand. This is 
continued until the cavity is quite filled, or even, if necessary, to some slight 
extent built out, the surface being rendered smooth and polished with a bur- 
nisher until it is quite set, which is generally in a very little (too short) a 
time." — Dental Surgery and Pathology. 

He also states, according to Kirk, that it is probably the most durable 
of all amalgams, but the most difficult to manipulate. Its surface changes to 
a black color, but as a rule does not stain the structure of the tooth. — Am. 
System of Dentistry. 



324 PRACTICAL DENTAL METALLURGY. 

TERNARY DENTAL AMALGAMS.— These are 
generally alloys composed of SILVER and TIN, com- 
minuted by filing or turning in a lathe, and amalgamated 
into a coherent mass with mercury. The components are, 
as a matter of course, subject to considerable variation, the 
proportions of silver and tin ranging from 75 parts of 
the silver to 25 of the tin, to 40 of the silver and 60 of 
the tin. The proportions of mercury range from about 
30 per cent, of mercury to about 70 per cent, of alloy, to 
equal parts by weight, or, exceptionally, a larger pro- 
portion of mercury may- be used. The comminuted 
alloy is amalgamated with the mercury by rubbing them 
together in the palm of the hand or in a wedgewood or 
ground-glass mortar until a more or less smooth and 
coherent mass is formed. When a considerable amount 
of mercury is used in the mixing, the excess is generally 
squeezed out through a muslin cloth or chamois skin. 
The mass, when packed together, acquires a metallic 
hardness within a few hours, and arrives at its full 
degree of hardness usually in twenty-four to forty-eight 
hours. It is then a hard, brittle mass that may be dressed 
with a file and polished as other metallic bodies. 

REQUISITE PROPERTIES OE A DENTAE AMAEGAM. 

1. Permanency of Form (exhibiting as little tendency to con- 

tract, expand or assume a spheroidal form as possible). 

2. Sufficient Density, Hardness, and Toughness to Resist At- 

trition. 

3. Strength and Sharpness of Edge. 

4. Complete Resistance to the Action of the Oral Secretions 

and Food. 

5. Freedom from Admixture with Any Metal Favorable to the 

Formation in the Mouth of Soluble Salts of an Injurious 
Character. 

6. Good Color. 

The first ternary dental-amalgam alloy was that formu- 
lated by Dr. Townsend consisting of silver 42 and tin 58 



CLASSIFIED AMALGAMS. 325 

parts. His formula has since been changed, however, to 
silver 44. 5, tin 54.5, and gold 1. Investigations and exper- 
iments then seem to demonstrate that those alloys con- 
taining more than 50 per cent, of silver gave better 
results. L,ater the scientific researches of Dr. Black* con- 
cerning the annealing of alloys gives evidence that the 
future ternary dental amalgam will closely approximate 
in formula silver 72.5 and tin 27.5. 

By the table of dental-amalgam alloys submitted on 
page 301 it may easily be seen that silver and tin form 
the basis of all amalgams used in dentistry. With a view 
to overcoming the imperfections in and disadvantages of 
this simple ternary amalgam, and increasing its tooth- 
conserving qualities, and, therefore, its usefulness, a vast 
amount of experimentation has been carried on by the 
profession and the supply concerns. Papers after papers 
have been written, published, and discussed, all of which 
have had a tendency to prove that there is good reason 
to believe that the addition of small proportions of one or 
more other metals will, in a measure, overcome the objec- 
tions inherent in an amalgam made of an alloy of silver 
and tin alone. 

QUARTERNARY, QUINARY, ETC., DENTAL 
AMALGAMS represent the basal alloy of silver and 
tin modified by the addition of one or more of the 
following metals in small proportions: Gold, plati- 
num, indium, copper, zinc, cadmium, bismuth, an- 
timony, and aluminum. 

GOLD is usually added to silver-tin dental-amalgam 
alloys to the extent of from 2 to 7 per cent. Dr. Bonwill 
regards a greater quantity very undesirable. f 

* See tables, p. 306. 

t Dental Cosmos, Vo\ XXIV, p. 422. 



326 PRACTICAL DENTAL METALLURGY. 

The addition of gold in the proportion of 5 per 
cent, to an alloy of silver 61.75 and tin 33.25, says 
Dr. Black, * "seems to give a little softer working 
property, and slows the setting of the mass. The 
mass has something more of the pasty character, 
and the fillings made of the annealed alloy are apt to 
finish very soft, the surface being so springy that it is 
difficult to make a good finish. It takes a little less 
mercury than the unmodified alloy, and the flow is a 
little more. The amalgam is very tough, and bears a 
heavy stress before crushing. The shrinkage-expansion 
range is reduced three points, "f 

Clinical records testify that it aids in maintaining a 
better color. 

PLATINUM. — The use of platinum in dental amal- 
gams was introduced by Thomas Fletcher.J He claims 
for amalgams containing it in proper proportions, perma- 
nency of form, and the property of rapidly hardening, 
but admits that such are excessively dirty to mix in the 
hand. Dr. Essig says it impairs an amalgam of silver 
and tin § 

"The appearance of the mass made of this alloy 
[silver 61.75, tin 33.25, and platinum 5] is very remark- 
able. That from the fresh-cut alloy is fairly white, but 
that from the annealed alloy is dark, and, in kneading, 
blackens the hand to an extraordinary degree with a 
grayish-blue black that is rather difficult to remove. 
The mass looks dirty and the finished filling is dark. 
The mass has a very peculiar softness to the feel under 
the instrument. The setting is slowed considerably. It 

* Dental Cosmos, Vol. XXXVIII, p. 988. 
f See table, p. 306. 

J Dental Metallurgy, Fletcher, p. 39. 
§ Dental Metallurgy, Essig, p. 52. 



CLASSIFIED AMALGAMS. 327 

flows badly. The shrinkage-expansion range is in- 
creased, and lies a little higher in the scale."* 

" When platinum is combined with silver, tin, and gold, 
its influence becomes apparent," explains Dr. Essig:f 
''With the proper proportion of mercury, it seems to 
confer upon such an alloy the property of almost instantly 
setting, as well as much greater hardness. Thus, it will 
be seen, that the qualities claimed for platinum per se 
belong in reality to the combination of tin, silver, gold, 
and platinum with mercury, since, if either one of the 
others is omitted, the platinum does not remain passive, 
but actually by its presence causes marked deterioration 
of qualities essential in a dental amalgam." 

Dr. Black's experiment upon such an amalgam demon- 
strates it as being very little better than the previous one: 

Silver 44.81, 

Tin 52.78, 

Gold 1.78, 

Platinum 62, and Mercury 39.18 per cent. 

Mixed in the hand and inserted by hand pressure. Mar- 
gins open all around from .3 to .8 thousandths of an 
inch. The same alloy with 37.45 mercury showed a 
flow of 19.81, and crushing strength of 225 pounds. 

COPPER. — One of the first dental amalgams was 
made from silver coin filings (about 9 parts silver to 1 of 
copper) by M. Taveau of Paris, in 1826, who called it 
" Silver Paste." It was afterwards introduced into 
America by Crawcouras " Royal Mineral Succedaneum." 
Such an amalgam expands greatly, and its intense black- 
ness is a great objection to its use. 

A very large percentage of the alloys found upon the 
market contains small proportions of copper, ranging 
usually from 3 to 8 per cent. 

* Black, Dental Cosmos, Vol. XXXVIII, p. 988. 
t Dental Metallurgy, p. 54. 



328 PRACTICAL DENTAL METALLURGY. 

With tin, copper yields a very white amalgam, by 
proper manipulation. There is, however, a tendency to 
soon discolor, which may be controlled, it is said, by a 
small proportion of gold. 

Of the alloy of silver 61.75, tin 33.25, and copper 5, 
Dr. Black says: " The fresh-cut, sets very quickly. The 
mass makes up soft, but it becomes hard almost immedi- 
ately it is left to itself. The annealed alloy makes a very 
soft, pleasant-working mass, and the setting is as slow as 
in the unmodified alloy. Expansion and the expansion- 
shrinkage range is markedly increased, the flow is dimin- 
ished, and the crushing stress is the greatest of the 
series."* 

ZINC 5, silver 61.75, and tin 33.25, Dr. Black says, 
forms f "a very remarkable amalgam for the amount 
and slowness of its expansion * * * in the fresh-cut 
alloy the expansion continued forty days, [reaching .0068 
of an inch]. The expansion in the filling from the an- 
nealed alloy [.0009] was not completed until thirty days 
had elapsed." He further explains that the mass is 
remarkable for its adhesion to the walls of the cavity; 
sets very quickly; that the zinc decreases the flow to the 
least of any of the series of amalgams examined (fresh-cut 
1.83, annealed 2.07 per cent.); that the filling has good 
resistance (290 and 345 pounds); and requires more mer- 
cury than the unmodified alloy of silver 65 and tin 35. 

When zinc is added to silver, tin, and gold alloys, it is 
said to prevent discoloration to a considerable extent. 
The addition, however, makes the amalgam "coarse- 
grained" and more difficult to amalgamate. ''Front- 
tooth alloys" usually contain zinc to maintain their 
whiteness. "A 'facing' — approximately, tin 55, silver 

* Dental Cosmos, Vol XXXVIII. p. 988. 
t Ibid. Vol. XXXVIII. p. 989. 



CLASSIFIED AMALGAMS. 329 

37, gold 5, zinc 3 — is that which at present is least 
liable to discolor."* 

Zinc is also added to amalgam alloys of silver, tin, and 
copper, but presents an amalgam little different from the 
above. 

BISMUTH.— An alloy of silver 61.75, tin 33.25, 
and bismuth 5 is remarkable for the readiness with 
which it amalgamates with mercury, and the small 
amount of mercury it requires. The working prop- 
erty of the amalgam is soft, the mass springy and 
very dark, the expansion and shrinkage range reduced, 
the flow increased, and the resistance to crushing reduced. 

ALUMINUM.— Dr. Black statesf that alloys contain- 
ing 5 per cent, of aluminum evolve considerable heat 
while setting, expand enormously, oxidize readily, and 
that a distinct crackling of gas-disengagement is heard 
during their packing. "The formation of aluminum 
amalgam is characterized by an exhibition of the affinity 
of aluminum for oxygen. Aluminum oxide is doubtless 
formed, which increases the volume of the amalgam 
mass." 

Cadmium, as a component of dental-amalgam alloys, 
has been very unsatisfactory, and should never be used. 
(See chapter on Cadmium.) 

For Antimony, see chapter devoted to that metal. 

ANALYSIS OF DENTAL AMALGAMS.— A per- 
fect familiarity with the composition of the alloys used in 
individual practice is indispensable, and it is also impor- 
tant, and, at times, exceedingly desirable, to be able to 
determine the composition of other alloys or old amalgam 
Plugs- 

* Flagg. Plastics and Plastic Fillings, p. 104. 
t Dental Cosmos, Vol. XXXVIII, p. 990. 



330 PRACTICAL DENTAI, METALLURGY. 

Analysis is accomplished by two means, known re- 
spectively as the dry and wet methods. 

The Dry Method consists principally of two parts: 

1st. A physical examination, noting weight, color of 
alloy, and discoloration, if any, and hardness. 

2d. Subjection to the heat of the blow-pipe either alone 
or in the presence of certain reagents. 

The Wet Method generally consists of dissolving the 
solid in some solvent, and precipitating the dissolved con- 
stituents separately as the simpler compounds of oxygen, 
sulphur, chlorine, etc. 

Before proceeding with the analysis of an old amalgam 
plug by the wet method, a careful study should be made 
of its weight, color, discoloration, hardness, etc. 

MERCURY. — It may then be weighed and placed in a 
hard glass tube or porcelain crucible and heated to a red 
heat, to drive off the mercury, the amount of which is 
determined by the difference in the first weight and 
that obtained after heating. 

This method is somewhat inaccurate, on account of 
the oxidation or volatilization of some of the constituents. 

The plug deprived of its mercury is placed in a mortar 
and finely divided; then a weighed quantity (usually 10 
or 20 grains) is transferred to a glass flask and sufficient 
chemically pure nitric acid added to more than dissolve 
it, by the aid of gentle heat. 

The powdered condition of the alloy is necessary; 
otherwise the metastannic acid formed by the action of 
nitric acid upon the tin, after a few moments, so protects 
the surface of the alloy, that it greatly retards, if not in a 
measure prevents, its complete solution. 

Much can be discerned qualitatively by the appearance 
of the solution. After the action of the acid is completed 
there will appear a residue in the bottom of the flask, 



CLASSIFIED AMALGAMS. 331 

with a clear supernatant liquid. If this liquid is colored 
a greenish-blue, copper is present. If the precipitated 
metastannic acid is white, or nearly so, gold and platinum 
in any considerable quantity need not be expected, as 
the presence of a very small amount of gold is sufficient 
to tint the metastannic acid purple, due to the formation 
of the purple of Cassius; and the presence of platinum 
is determined by a black powder, small particles of metal- 
lic, platinum mixed with the metastannic acid. Very 
small quantities of this metal are, however, dissolved in 
nitric acid, in the presence of a large excess of silver. 

TIN. — -The contents of the flask should then be filtered, 
the filtrate preserved, and the precipitate thoroughly 
washed with distilled water, dried, the metastannic acid 
(H 10 Sn 5 O l5 ) rendered anhydrous (Sn0 2 ) by calcining 
at a red heat, and then weighed, — 78.66 per cent, of the 
mass representing the amount of tin in the alloy. 

ANTIMONY. — If there be any reason to suspect the 
presence of antimony in the alloy, the dioxide of tin 
(Sn0 2 ) should be fused in a silver crucible with sodium 
hydrate (NaHO) by which the antimonate (NaSb0 2 ) and 
stannate (Na 2 Sn0 3 ) of sodium are formed. The fused 
mass is now digested and disintegrated in cold water, and 
filtered. If antimony be present, it will be caught on 
the filter paper as the antimonate of sodium, while the 
soluble stannate of sodium passes through with the 
filtrate. The antimonate should now be washed with 
distilled water, dried and weighed — 68.92 percent, of the 
mass representing the amount of antimony in the alloy. 

SILVER. — The filtrate which was originally the super- 
natant liquid in the flask, should now be diluted some- 
what, and hydrochloric acid added until no more 
precipitate (silver chloride) is formed, when the whole 
should be filtered, the precipitated silver chloride remain- 



332 PRACTICAL DENTAL METALLURGY. 

ing on the filter paper, washed with distilled water, dried 
and weighed — 75.26 per cent, of the mass representing 
the amount of silver present in the alloy. 

COPPER. — The original supernatant liquid in the flask 
is now treated to sulphuretted hydrogen. The copper 
and cadmium are thrown down as sulphides. The 
copper sulphide is black, while that of cadmium is lemon 
yellow. The contents of the flask are again filtered, and 
the copper and cadmium sulphides caughf upon the filter 
paper; these are washed with distilled water and treated 
with dilute sulphuric acid, the cadmium sulphide being 
dissolved. All is again filtered; the dissolved cadmium 
sulphide passing through, and the copper sulphide re- 
maining upon the filter, should be washed, dried, and 
weighed — 66.49 per cent, of the mass representing the 
amount of copper present in the alloy. 

CADMIUM. — The cadmium sulphide may be thrown 
down now with potassium hydrate as cadmium hy- 
droxide, Cd2HO, dehydrated by heating, and weighed 
as cadmium oxide, CdO — 87.49 per cent, of the mass 
representing the amount of cadmium in the alloy. 

ZINC. — From the original solution the zinc may be 
separated as the carbonate (ZnC0 3 ) by adding one of the 
alkaline carbonates. It is then washed, heated to red- 
ness, and weighed as the pure oxide of zinc, ZnO — 80.24 
per cent, of the mass representing the amount of zinc in 
the alloy. 

GOLD. — Probably the most practical manner of deter- 
mining the amount of gold in a dental-amalgam alloy of 
approximately unknown composition is as follows: After 
drying and accurately weighing the insoluble residue of 
metallic platinum and precipitated compounds of gold 
and tin, obtained upon dissolving the original alloy or 
plug in pure nitric acid, it should be fused with potas- 



CLASSIFIED AMALGAMS. 333 

sium carbonate and cyanide; the tin oxide is dissolved 
by the flux, and the resulting button is composed of gold 
and platinum. This should now be rolled to a very thin 
ribbon, cut up and digested in aqua regia (see chapter 
on gold), forming the soluble chlorides of gold and 
platinum. The chlorides thus formed are then dissolved 
in a sufficient quantity of distilled water, from which 
the gold is precipitated in the metallic state by the 
addition of a solution of oxalic acid or the sulphate of. 
iron . It is then collected by filtration, fused, and weighed. 
PLATINUM. — The platinum in the remaining solu- 
tion is thrown down as ammonio-platinic chloride 
(H 4 NCl) 2 PtCl 4 , by the addition of sal ammoniac, washed, 
dried, and weighed as such — 44.17 per cent, of the mass 
representing the amount of platinum in the alloy. 

EXPERIMENTS. 

No. 73. — The student should prepare a small quantity of copper amalgam 
by any one of the several methods. 

No. 74. — Prepare a dental-amalgam alloy of silver and tin. 

No. 75. — Prepare a dental-amalgam alloy of silver, tin, and gold. 

No. 76. — Prepare a dental-amalgam alloy of silver, tin, and copper. 

No. 77. — Prepare a dental-amalgam alloy of silver, tin, and platinum. 

No. 78 — Prepare a dental-amalgam alloy of silver, tin, and zinc. 

No. 79. — Prepare a dental-amalgam alloy of silver, tin, and bismuth. 

No. 80. — Prepare a dental-amalgam alloy of silver, tin, copper, and gold. 

No. 81.— Prepare a dental-amalgam alloy of silver, tin, copper, and plati- 
num. 

No. 82. — Prepare a dental-amalgam alloy of silver, tin, copper, and zinc. 

No. 83. — Prepare a dental-amalgam alloy of silver, tin, gold, and platinum. 

No. 84. — Prepare a dental-amalgam alloy of silver, tin, gold, and zinc. 

No. 85 — Prepare a dental-amalgam alloy of silver, tin, gold, and bismuth. 

No. 86. — Prepare a dental-amalgam alloy of silver, tin, gold, and anti- 
mony. 



Kach student should have the preparation of some one alloy, at least, 
which, after casting in a suitable ingot, should be comminuted and equally 
divided into four parts; two parts should be amalgamated fresh-cut in the fol- 
lowing manner: a portion mixed with an excess of mercury in a mortar by 
thorough rubbing; and a portion mixed with an excess of mercury in the 
hand. 

Each of these two mixes kept separately should be divided into three por- 
tions. 



334 PRACTICAL DENTAL METALLURGY. 

From portion No. 1 mortar-mix, squeeze the mercury out between finger 
and thumb. 

From portion No. 2 mortax-mix, squeeze the mercury out through chamois 
skin till moderately dry. 

From portion No. 3, mortar-mix, squeeze the mercury out through chamois 
skin till very dry. 

Prepare the three portions of the hand-mix in the same manner, and insert 
all six portions in as many test-tubes* with the same carefulness of manner 
as in filling teeth. When the amalgam thus inserted has begun to set in the 
glass tubes, fill the remaining portion of the tube with a very thin solution 
or red ink. Others may place tube and all in a solution of sulphuretted 
hydrogen. These are to remain until the next meeting of the class, when 
any shrinkage or expansion is to be noted, together with the discoloration, 
hardness, edge-strength, etc. 

Before the next hour for experimental work in the laboratory the two 
remaining portions of comminuted alloy should be aged or annealed as 
follows: One portion in an ordinary test-tube (5xfg) should be placed in a 
boiling water-bath for ten or fifteen minutes, and the second portion also in a 
sealed test-tube may be placed close to the glass on the inside of the window 
where the warmth of the sun may reach it during several days. 

During the next laboratory hour these two portions of annealed alloy 
should be amalgamed with mercury and the amalgam thus formed inserted in 
separate test-tubes* and allowed to fully harden, after which they should be 
tested similarly to the manner of the six previous mixes. 

No. 87.— Analysis of amalgam: Make quantitative (or only qualitative) ex- 
amination of some known dental-amalgam alloy. 

No. 88. — Make quantitative (or only qualitative) examination of an old 
amalgam plug of unknown composition. 

Note. — In performing these experiments the student should be allowed to 
vise his own judgment, grounded on his reading, as to the proportion of each 
metal constituent of the amalgam alloy. As most formulae are expressed 
centesimally the author has been in the habit of instructing students to 
prepare one-tenth of the formulated amount expressed in parts: thus a 
formula written silver 65 and tin 35 (dwts. or parts) one-tenth would be silver 
6.5 and tin 3.5 (dwts. or parts); one-tenth the original amount or 10 dwts. being 
quite sufficient. 

The metals should be accurately weighed, melted together as suggested in 
the chapter on Alloys, poured into an ingot mold and cast suitable for filing or 
turning, cleaned of borax and reweighed. The student should keep in mind 
the formula, manner of forming the alloy, and the loss, if any, in forming it, 
together with the date and any other circumstance connected with the 
making, thought to be of value. 

The student may be required to prepare a thesis on amalgam in such a 
manner and of such length as the instructor may deem of the best advantage 
to the student. 

* The test-tubes provided for each student should be of ordinary size glass- 
tubing cut in pieces of one-half inch in length. 



ADDENDUM: 

A Reference to Collateral Literature upon the 
Various Subjects Treated. 



A. 

ALLOYS. 



Brannt, Metallic Alloys. 

Essig, Dental Metallurgy, p. 34. 

Fletcher, Dental Metallurgy. 

Kirk, American System of Dentistry, Vol. Ill, p. 795. 

Makins, Metallurgy, p. 53. 

Phillips, Metallurgy. 

ALUMINUM. 

Amalgam, Dental Cosmos, Vol, XXXV, p. 1050; Vol. XXXIII, 
p. 481. 

Base for Artificial Dentures, Dental Cosmos, Vol. XXXI, p. 950. 

Base for Artificial Dentures, A. H. Forbes, American System of Den- 
tistry, Vol. II, p. 725 

Cast Bridge-Work, Dental Cosmos, Vol. XXXIII, p. 1021. 

Cast Dentures, Dental Cosmos, Vol. XXXIII, p. 481. 

Foil, Dental Cosmos, Vol. XXXI, p. 645. 

Solder, Dental Cosmos, Vol. XXXI, p. 576; Vol. XXXV, pp. 161, 
499, 668 ; Vol. XXXVI, p. 437. 

Brannt, Metallic Alloys, pp. 48, 261. 

Essig, Dental Metalhirgy, p. 238. 

Fletcher, Dental'^Metallurgy, p. 57. 

Gore, Electro- Metallurgy, p. 289. 

Kirk, Dental Metallurgy, American System of Dentistry, Vol. Ill, 
p. 932. 

Makins, Metallurgy, p. 529. 

Note. — The object of these references is to direct the collateral study or 
reading of the student; that the text may be more clearly understood, and 
that greater knowledge may be obtained on the subject than is possible to be 
gained from a text-book solely. 

To the furtherance of this, reading clubs should be started among the 
students. 



336 PRACTICAL DENTAL METALLURGY. 

AMALGAMS. 

By B. F. Arrington, Dental Cosmos, Vol. XXXII, p. 795. 

By Theo. Johnstone, Dental Cosmos, Vol. XXXV, p. 450. 

By Edmund Kells, Jr., Dental Cosmos, Vol. XXXVI, p. 290. 

By H. B. Tileston, Items of Interest, Vol. XIX, p. 572. 

As a Filling Material, B. T. Darby, Dental Cosmos, Vol. XXXVI, 
p. 178. 

As a Filling Material, Sigel Roush, Dental Cosmos, Vol. XXXVI, 
p. 428. 

As a Filling Material, Edw. Page, International Dental Jr., Vol. 
XIV, p. 572. 

As Chemical Compounds, H. H. Burchard, Dental Cosmos, Vol. 
XXXVII, p. 989. 

As a Restorer in Extensive Loss of Coronal Surface, W. B. Sher- 
man, Dental Cosmos, Vol. XXXV, p. 1107. 

An Investigation of the Physical Character of the Human Teeth in 
Relation to their Diseases, and to Practical Dental Opera- 
tions, together with the Physical Characters of Filling 
Materials, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 553. 

Cadmium, use of in, E. T. Darby, Dental Cosmo 1 :, Vol. XXXVI, 
p. 178. 

Combining, and Gold, E. A. Royce, Dental Review, Vol. VI., p. 765. 

Copper, P. J. Kesler, Dental Review, Vol. VI., p. 773. 

Copper, W. H. Truman, Dental Cosmos, Vol. XXXII, p. 476. 

Copper, Dental Review, Vol. VII, p. 663. 

Copper for Filling Cavities in Bone, Pacific Coast Dentist, Vol. I, 
p. 245. 

Copper Amalgam, Discoloration of, International Dental Jr., Vol. 
XVIII, p. 315. 

Copper, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 637. 

Dental, A. C. Hewitt, Dental Review, Vol. X, p. 176. 

Dental and Amalgamation, D. R. Stubblefield, Dental Cosmos, Vol. 
XXXH, p. 910. 

Expansion of, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 568. 

Effect of Oxidation of, G. V. Black, Dental Cosmos, Vol. XXXVIII, 
p. 43. 

Finishing of, Dental Review, Vol. VIII, p. 208. 

Mixing of, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 561. 

Mercurial Poisoning by, Dental Cosmos, Vol. XXXIV, p. 828. 

Physical Properties of, G. V. Black, Dental Cosmos, Vol. XXXVII, 
p. 554. 



ADDENDUM. 337 



Physical Properties of Silver-Tin Amalgams, G. V. Black, Dental 

Cosmos, Vol. XXXVIII, p. 965. 
Packing of, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 659. 
Plastics, Denial Review, Vol. VI, p. 793. 
Selection of Cases for, Ottolengui, Dental Cosmos, Vol. XXXIV, 

p. 640. 
Silver and Tin, G. V. Black, Dental Cosmos, Vol. XXXVII, p. 554. 
Silver and Tin, Contraction and Expansion, G. V. Black, Dental 

Cosmos, Vol. XXXVII, p. 637. 
Spheroiding of, G. V. Black, Dental Cosmos, Vol. XXXVII, pp. 

569, 642. 
Some Principles Relating to, B. C. Kirk, International Dental Jr. 

Vol. XVI, p. 214, 
Tests of, Dental Cosmos, Vol. XXXII, p. 752. 
The Dental Filling, Jos. Head, Dental Cosmos, Vol. XXXVIII, 

p. 550. 
Use of, Dental Review, Vol. VIII, p. 248. 
Use from a Practical Standpoint, W. B. Halsey, Dental Cosmos, 

Vol. XXXVII, p 275. 
Use in Children's Teeth, J. Y. Crawford, Dental Cosmos, Vol. 

XXXVII, p. 444. 
Washing, F. W. Prichett, Denial Review, Vol. X, p. 46. 
Brannt, Metallic Alloys, p. 349. 
Bssig, Dental Metallurgy, p. 46. 
Flagg, Plastics and Plastic Filling. 
Fletcher, Dental Metallurgy. 

Kirk, American System of Dentistry, Vol. Ill, p. 804. 
Makins, Metallurgy. 

Mitchell, Dental Chemistry and Metallurgy, p. 138. 
Plastic Materials for Filling Teeth, A. G. Bennett, American System 

of Dentistry, Vol. II, p. 218. 

ANTIMONY. 
Gore, p. 103. 

Makins, Metallurgy, p. 384. 
Mitchell, Dental Chemistry and Metallurgy , 2d edition, p. 172. 

B. 

BISMUTH. 



Brannt, Metallic Alloys, p. 301. 
-Fletcher, Dental Metallurgy, p. 64. 



338 PRACTICAL DENTAL METALLURGY. 

Gore, Electro- Metallurgy, p. 111. 

Kirk, American System of Dentistry, Vol. Ill, p. 928. 

Mitchell, Dental Chemistry and Metallurgy, p. 160. 

c. 

CADMIUM. 

In Dental- Amalgam Alloys, F. H. Fales, Dental Cosmos, Vol. 

XXXI, p. 660. 

In Dental-Amalgam Alloys, F. T. Darby, Dental Cosmos, Vol. 

XXXVI, p. 178. 
In Dental-Amalgam Alloys, Flagg, Plastics and Plastic Pilling, (1st 

edition), p. 54. 
Fletcher, Dental Metallurgy, p. 70. 
In Dental-Amalgam Alloys, Fletcher, Practical Dental Metallurgy^ 

p. 71. 
Kirk, American System of Dentistry, Vol. Ill, p. 927. 
Kssig, Dental Metallurgy, p. 236. 
Mitchell, Dental Chemistry and Metalhirgy, p. 130. 
Makins, Metallurgy, p. 525. 

COPPER. 
Amalgam of, Dental Cosmos, Vol. XXXI, pp. 265, 918; Vol. 

XXXII, pp. 388, 476, 912; Vol. XXXIII, pp. 58, 383; Vol. 
XXXV, pp. 26, 129: Vol. XXXVI, pp. 120, 180, 299, 830. 

Amalgam of, Items of Interest, Vol. IX, p. 399. 

As a Filling Material, Dental Cosmos, Vol. XXXII, p. 718. 

Canal Points, Dental Cosmos, Vol. XXXII, p. 751; Vol. XXXV, 

p. 204. 
Deposit on the Teeth, Dental Cosmos, Vol. XXXVI, p. 265. 
In Amalgam Alloys, Flagg, Plastics and Plastic Filling, p. 48. 
In Regulating, Dental Cosmos, Vol. XXXIV, p. 1001. 
Pulp Caps, Dental Cosmos, Vol. XXXIII, p. 62. 

To Finish Amalgam Fillings, Dental Cosmos, Vol. XXXVI, p. 301. 
Use in the Mouth, Dental Cosmos, Vol. XXXII, p. 549. 
Wire in the Mouth, Dental Cosmos, Vol. XXXIII, pp. 805, 1070, 
Brannt, Metallic Alloys, p. 90-97. 
Essig, Dental Metallurgy, p. 221. 
Fletcher, Dental Metallurgy, p. 60. 
Gore, Electro- Metallurgy, p. 198. 
Kirk, American System of Dentistry , p. 908. 
Mitchell, Dental Chemistry and Metallurgy , p. 133. 



ADDENDUM. 339 



G. 

GOLD. 

As a Filling Material, Ottolengui, Dental Cosmos, Vol. XXXIV, 

pp. 131, 191, 377, 819. 
As a Filling Material, W. D. Miller, Dental Cosmos, Vol. XXXIV, 

p. 552. 
Alloys, Formulae for, Dental Cosmos, Vol. XXXV, pp. 161, 246. 
And Amalgam as a Base for Filling, International Dental Jr., Vol. 

XIV, p. 170. 
Beating, Dental Review, Vol. X, p. 257. 
Cohesive and Non-Cohesive, I. C. Curtis, Dental Cosmos, Vol. 

XXXIV, p. 201. 
Cohesive Property of Gold, S. H. Guilford, Dental Cosmos, Vol. 

XXXIV, p. 799. 
(Cohesive) Properties of Gold, Dental Cosmos, Vol. XXXVIII, 

p. 616. 
Combining Amalgam and Gold, Dental Review, Vol. VI, p. 765. 
Combination of Cohesive and Non-Cohesive, Dental Reviezv, Vol. 

VII, p. 633. 
Crystal Mat Gold, E. C. Kirk, International Dental Jr., Vol. XLV, 

p. 97. 
Crystal Gold, Watts, F. S. Hopkins, International Dental Jr., Vol. 

XIV, p. 359. 
Crystalline vs. Foils, Dental Cosmos, Vol. XXXII, p. 281. 
Cylinders, L. C. F. Hugo, Dental Cosmos, Vol. XXXVI, p. 433. 
Flow of under Stress, G. V. Black, Dental Cosmos, Vol. XXXVII, 

p. 743. 
Filling Materials, Dental Revietv, Vol. VIII, p. 889. 
Manipulation of Gold for Fillings, Dental Review, Vol. VI, p. 366. 
Non-Cohesive, Its Merits and Manipulation, Items of Interest, Vol. 

XIX, p. 85. 
Physical Properties of, Dental Cosmos, Vol. XXXVII, p. 740. 
Relative Value of Gold and Amalgam, Dental Review, Vol. VIII, 

p. 363. 
Soft Foils and Plastic Stoppings, C. B. Frances, International 

Dental Jr., Vol. XV, p. 356. 
Solida Gold, Theo. Frick, International Dental Jr., Vol. XVII, 

p. 372. 
Some Thoughts on the Behavior, Dental Review, Vol. VIII, 
p. 320. 



340 PRACTICAL DENTAL METALLURGY. 

Spreading Properties, Dental Revietu, Vol. VII, p. 937. 

Submarine, Fillings, Items of Interest ', Vol. XIX, p. 379. 

Tin and Gold, Dental Review, Vol. X, p. 94. 

Brannt, Metallic Alloys, p. 324. 

Burchard, Operative Dentistry, Kirk, p. 219. 

Essig, Dental Metallurgy, p. 113. 

Fletcher, Dental Metallurgy, p. 26. 

Gore, Electro-Metallurgy, p. 179. 

Kirk, American System of Dentistry, Vol. Ill, p. 830. 

Makins, Metallurgy, p. 220. 

I. 

IRON. 

Brannt, Metallic Alloys, p. 379. 

Ede, Geo., Management of Steel. 

Essig, Dental Metallurgy, p. 203. 

Fletcher, Dental Metallurgy, p. 46. 

Kirk, American System of Dentistry, Vol. Ill, p. 895. 

Makins, Metallurgy, p. 410. 

L- 

LEAD. 

Deposit on Teeth, Dental Cosmos, Vol. XXXVI, p. 271. 

Discoloring Gums, Dental Cosmos, XXXV, p. 150. 

Fillings in Carious Teeth, Dental Cosmos, Vol. XXXIII, p. 1083. 

In Root Filling, Vol. XXXI, pp. 534, 802; Vol. XXXII, p. 48, 
Vol. XXX IV, 820. 

In Pulp Capping, Dental Cosmos, Vol. XXXIII, p. 175. 

In Contaminating Drugs, Dental Review, Vol. VI, p. 988. 

In Counter Dies, Haskell, Students Manual, p. 17. 

Implantation of Metallic Capsules in the Human Jaw, Dental Cos- 
mos, Vol. XXXI, p. 232. 

Poisoning, Dental Cosmos, Vol. XXXIV, pp. 928, 832. 

Brannt, Metallic Alloys, p. 284. 

Essig, Dental Metallurgy, p. 246. 

Fletcher, Dental Metallurgy, p. 62. 

Gore, Electro-Metallurgy , p. 79. 

Kirk, A?nerican System of Dentistry, Vol. Ill, p. 919. 



ADDENDUM. 341 



M. 

MERCURY. 

Concerning Vulcanite, C. A. Allen, Dental Cosmo?, Vol., XXXVIII, 

p. 727. 
Essig, Dental Metallurgy, p. 211. 
Fletcher, Dental Metallurgy , p. 52. 
Kirk, American System of Dentistry, Vol. Ill, p. 903. 
Makins, Metallurgy, p. 128. 

P. 

PALLADIUM. 

Essig, Dental Metallurgy, p. 199. 
Fletcher, Dental Metallurgy, p. 41. 
Gore, Electro-Metallurgy , p. 114. 
Kirk, American System of Dentistry , p. 892. 

PLATINUM. 

Alloys for Plate and Clasp Metal, Richardson, Mechanical Dentistry, 

pp. 56, 57. 
And Gold as a Filling Material, Dental Cosmos, Vol. XXXVI, 

p. 196.; Vol. XXXVII, p. 956. 
In Electrical Heating Devices, Dental Cosmos, Vol. XXXVII, 

p. 1016. 
Melting by Electricity, Dental Cosmos, Vol. XXXVI, p. 714. 
Properties and Use of, Items of Interest, Vol. XIX, p. 460. 
Pins Used in Mineral Teeth, A Defect in, Dental Review, Vol. XI, 

p. 15. 
Brannt, Metallic Alloys, p. 337. 
Essig, Dental Metallurgy, p. 184. 
Fletcher, Dental Metallurgy, p. 35. 
Gore Electro-Metallurgy, p. 118. 
Kirk, American Syste?n of Dentistry, Vol. Ill, p. 883. 

s. 

SILVER. 

Electro-Deposition of, J. D. Hodgen, Trans. Cal. State Dental 

Assn., 21st and 22d Annual Sessions, p. 213. 
Brannt, Metallic Alloys, p. 309. 
Essig, Dental Metallurgy, p. 166. 



342 PRACTICAL DENTAL METALLURGY. 

Fletcher, Dental Metallurgy, p. 32. 

Gore, Electro- Metallurgy, p. 146. 

Kirk, American System of Dentistry, Vol. Ill, p. 868. 

Makins, Metallurgy, p. 150. 

- SOLDER- 
Soldering, Dental Review, Vol. XI, p. 155. 

T. 

TIN. 

As a Filling Material, Dental Cosmos, Vol. XXXII, p. 711; Vol. 

XXXV, p. 775. 
And Gold as a Filling Material, Dental Cosmos, Vol. XXXIII, p. 52; 

Vol. XXXIX, p. 391. 
Model for Vulcanizing, Dental Cosmos, Vol. XXXV, p. 163. 
Therapeutic Effects of Tin Fillings, Dental Cosmos, Vol. XXXI, 

p. 802. 
Brannt, Metallic Alloys, p. 271. 
Essig, Dental Metallurgy, p. 249. 
Fletcher, Dental Metallurgy, p. 44. 
Gore, Electro- Metallurgy, p. 263. 

Kirk, American System of Dentistry, Vol. Ill, p. 915. 
Makins, Metallurgy, p. 491. 

z. 

ZINC. 

Essig, Dental Metallurgy, p. 228. 

Fletcher, Dental Metallurgy, p. 66. 

Gore, Electro- Metallurgy, p. 274. 

Kirk, American System of Dentistry, Vol. Ill, p. 921. 

Makins, Metallurgy, p. 510. 



INDEX. 



Page 

Alloys 83 

Aluminum 162, 191 

Annealing 90 

Antimony .. 104, 121, 129, 159 

Arsenic 105, 159 

Bean's , 121 

Bismuth Ill, 128, 159 

Cadmium 150, 151, 245 

Carroll's 188 

Color of 87 

Conductivity of 89 

Copper Ill, 122, 128, 

158, 193, 221, 245, 278, 282 

Darcet's Fusible 130 

Decomposition of 89 

Dental-Amalgam 296 

Ductility of 87 

Fusibility of 88 

Gold 

Ill, 120, 144, 158, 192, 
221, 231, 236, 244, 277, 285 
Hodgen's Dental - Amal- 
gam Alloy 302 

Hodgen's Fusible 130 

Influence of Certain Met- 
als in 92 

Iridium 230, 244 

Iron... 123, 145, 159, 183, 196 

Lead 102, 

123, 128, 129, 145, 159, 245 

Lipowitz's 151 

Malleability of 87 

Mathew's Fusible 130 

Newton's 129 

Nickel 161 

Onion's Fusible 129 

Oxidation of 91 

Palladium . . . 103, 120, 235 

Platinum 103, 

120, 144, 159, 231, 244, 282 

Preparation of. 95 

Rees's 121 

Rose's Fusible 129 

Rules for Compounding 

Gold 285 

Silver 

103, 121, 144, 159, 192, 
221, 231, 236, 245, 277, 282 

Sonorousness of 89 

Specific Gravity of. 86 

Tempering 91 



Page 
Alloys — Continued, 

Tenacity of. 87 

Theory of 83 

Tin 104, 111, 

120, 128, 129, 146, 196, 245 

Wood's 129, 151 

Zinc. 128, 144, 159, 196, 222 

Aluminum 185 

Action of Acids on 191 

Action of Alkalis on 191 

Alloys 191 

Aluminum Solder. 194 

Blow-Pipe Analysis 196 

Casting 189 

Compound with Oxygen . 190 
Electro-Deposition of . . . . 197 

Foil 190 

In Dentistry 187 

In the Arts 187 

Occurrence 185 

Properties 186 

Reduction 185 

Tests for, in Solution .... 196 

Amalgams 293 

A Dental— Definition 296 

Ageing 304 

Alloys, Dental — Defini- 
tion. 296 

Aluminum 192, 329 

Amalgamation 308 

Analysis of Antimony in 331 
" Cadmium in . 331 
" Copper in ... 331 

" Dental 329 

" Goldin 331 

" Mercury in .. 330 
" Platinum in.. 332 

" Silver in 331 

" " Tin in 331 

" Zinc in 331 

Antimony Ill 

Binary 318 

Bismuth 131, 329 

Cadmium 150, 323 

Chandler's Method for 
Making Copper Amal- 
gam 321 

Classified 318 

Comminution 303 

Composition of some well- 
known Alloys 301 



344 



PRACTICAL DENTAL METALLURGY. 



Page 
Amalgams — Continued. 

Conductivity 317 

Copper. 153, 163,209,320, 327 

Definition of 293 

Discoloration 317 

Edge Strength 316 

Expansion and Contrac- 
tion 310 

Facing, Alloy 328 

Flow 315 

Formation of 299 

Gold 248 320, 325 

History 297 

Hodgen's, University Cal. 
College of Dentistrv.. . 302 

In the Arts " 295 

Iridium 230 

Iron 183 

Kirk's Method of Mak- 
ing Copper Amalgam. 209 

Lead 102 

Means of P'orming 294 

Mercury Required in ... . 307 

Native 199, 248, 249, 294 

Palladium 235, 322 

Platinum 244, 322, 326 

Quarternary ...... 325 

Quinary 325 

Requisite Properties of a 

Dental 324 

Resistance to Stress 313 

Silver 204, 318 

Silver-Tin 324 

Spheroiding 312 

Table of Modified Alloys 306 
Table of Silver-Tin Alloys 306 

Ternary Dental 324 

Tin 120, 319 

Tin-Silver 324 

Washing 317 

Zinc 144, 322, 328 

Amalgamation of Silver. . . 212 

Alkali, An 38 

Antimony 108 

Action of Acids on . ... 110 

Alloys Ill 

Electro-Deposition of. . . 113 

Occurrence 108 

Oxides 109 

Properties 109 

Reduction 108 



Page 
Antimony — Continued. 

Test for, in Solution 112 

Argentiferous Galena 213 

Arnold's Iron Alloy 183 

Babbitt Metal 112, 122 

Bauxite 50 

Bean's Alloy 121 

Bell Metal 122 

Bellows 78 

Bismuth 125 

Action of Acids on 127 

Alloys 128 

Blow-Pipe Analysis of. . . 132 

Electro-Deposition of . . . . 133 

Occurrence 125 

Oxides 127 

Properties 126 

Reduction 125 

Tests for, in Solution 132 

B^ow-Pipks 69 

Compound 76, 77 

Flame of 72 

Gasoline 74 

Self-Acting 75 

Simple 69 

Use of 72 

Borax 53 

Brass 159 

Cast 160 

Sheet 160 

Wire 160 

Britannia Metal. ...112,121 

Bromides 46 

Metallic 46 

Reduction of 47 

Bronze 122 

Aluminum 162, 193 

Tin 122 

Cadmium 148 

Action of Acids on 149 

Alloys 150 

Compounds of 149 

Compounds with Oxygen 149 

Electro-Deposition of. . . 152 

Occurrence 148 

Properties 148 

Reduction 148 

Tests for, in Solution 152 

Calcination 14 

Calorific Energy, Table of. 57 

Calorific Energy . 56 

Calorific Intensity 57 



INDEX. 



345 



Page 

Carat 280 

Carroll's Alloy 188 

Cementation 15 

Cements 140 

Mixing 142 

Oxychloride 140 

Oxysulphate 142 

Phosphate 140 

Charcoal 57 

Chemistry 9 

Chlorides 44 

Metallic 44 

Reduction of 45 

Cinnabar 198 

Cliche Metal 112, 151 

Coal 57 

Coal Gas 59 

Coins 159 

Copper 161 

Gold 278 

Mexican 221 

Nickel 161 

Silver 221 

Coke 58 

Colcothar 182 

Copper 153 

Action of Acids on 157 

Alloys 158 

Blow-Pipe, Analysis of. . 163 

Commercial 154 

Compounds with Oxygen 157 

Dental Applications 156 

Dental- Amalgam Alloys 

158, 163 

Electro-Deposition of ... 163 

Occurrence 153 

Properties 155 

Pure 155 

Reduction 153 

Test for, in Solution 163 

Corundum 190 

Crucibles 51 

Cupellation 215 

Cyanides 48 

Metallic 48 

Darcet's Alloy 130 

Deoxidizing Agents. 37 

Dies 136 

Counter 137 

Dinas Clay 50 



Page 
Discoloration of Gold Fill- 
ings 274 

Distillation 14 

Dolomite 50 

Dry Process 15 

Dutch Metal 160 

Electro-Deposition 

Of Gold 290 

Of Silver 224 

Dentures bv 226 

Solutions for 225 

Elements 9 

Gaseous 18 

Liquid 18 

Metallic 12 

Solid 18 

Table of. 10, 11 

Emery 191 

Feldspar 191 

Fire-Brick 50 

Fire-Clay 50 

Fire-Gilding 296 

Flame 71 

Blow-Pipe 72 

Candle 71 

Oxidizing 72 

Reducing 72 

Fluorides 47 

Metallic 47 

Fluxfs 53 

Black 55 

Borax 53 

Liquid 55 

Prepared 55 

Powder 55 

Foil.... 271, 268 

Aluminum 190 

Cohesive 272 

Corrugated 268 

Crvstal 270 

Cylinders 269 

Non-cohesive 272 

Platinum and Gold 270 

Properties 271 

Purity of. 273 

Rolled 269 

Semi-cohesive 273 

Tin 117 

Fuel 55 

Furnaces 60 



346 



PRACTICAL DENTAL METALLURGY. 



Page 

Furnaces— Continued. 

Air 62 

Blast 61 

Crucible 66, 67, 62 

Continuous-Gum 63 

Dental Laboratory 63 

Draught 62 

Gasoline 65 

Muffle 63 

Reverberatory 62 

Gas, Coal 59 

Gasoline 59 

Ganister 50 

Gangue 12 

German Silver 161 

Gold Beating 266 

Gold 246 

Action of Acids on. , 275 

Alloys 277 

Alloys, Rules for Comput- 
ing and Compounding 285 

Annealing . 270 

Beating 266 

Caratation 279, 280 

Chemically Pure 259 

Clasp 283 

Colored 278, 280 

Compounds of with Oxy- 
gen 274 

Corrugated Foil 268 

Crown 283 

Cylinders 269 

Crystal 270 

Distribution of 249 

Dust 246 

Electro-Deposition of . . . . 290 

Extraction 249 

Float 246 

Foil 268 

Jewelers' 279 

Mining 249 

Native 246 

Nuggets of. 246 

Occurrence 246 

Placers 249 

Plate 281 

Properties 265 

Refining 253 

' ' by Roasting Process 253 
" " Parting " 256 



Page 
Gold— Continued. 

Rolled 269 

Standard 278 

Tests for in Solution 290 

Graphite 50 

Haskell's Babbitt Metal. ... 122 

Hodgen's Fusible Alloy . . . 130 

Hydroxides 38 

Hydrogen, Disposable 56 

Ingot Molds 81 

Iodides 47 

Metallic 47 

Iridium 229 

Action of Acids on 230 

Alloys 230 

Compounds with Oxygen 330 

Occurrence 229 

Properties 229 

Reduction 229 

Iron 165 

Action of Acids on 182 

Alloys 183 

Bar 172 

Blooms 171 

Carburized , 176 

Cast....... 170, 177 

Chromium in 175 

Compounds with Oxygen 181 

Magnetic 166 

Manganese in 176 

Meteoric 165 

Modifications of. 170 

Occurrence 165 

Ores of 165 

Pig . .... 170 

Properties of 169 

Puddling 171 

Pyrites 166 

Reduction of 167 

Test for, in Solution 184 

Wrought 171, 177 

Kaolin 50, 191 

Lamps 73 

Gas 75 

Gasoline 74 

Oil 73 

Spirit 74 

Lead 98 

Action of Acid on 101 



INDEX. 



347 



Page 
Lead — Continued. 

Action of Aqueous Re- 
agents on 102 

Alloys 102 

Blow-Pipe Analysis 106 

Compounds with Oxygen 100 

Dental Applications 100 

Desilvering 214 

Electro-Deposition of . . . 107 

Occurrence 98 

Properties 99 

Red 101 

Reduction of 98 

Tests for, in Solution .... 105 

Lipowitz's Alloy 151 

Loadstone 182 

M a r 1 i e ' s Non-oxidizable 

Alloy 184 

Mathews' Fusible Alloy... 130 

Melting Pots 68 

Mercury 198 

Action of Acids on 203 

Alloys 204 

Blow-Pipe Analysis 209 

Compounds with Oxygen 202 

Detection of Bismuth in . 200 

Detection of Lead in ... . 200 

Detection of Tin in 200 

Electro-Deposition 209 

In Medicine 201 

Occurrence 198 

Poisoning 202 

Properties of 201 

Pure 199 

Reduction 199 

Test for, in Solution 208 

Use in Dentistry 202 

Uses of 201 

Metallurgy 12 

Metal 19 

Annealing 24 

Base 16 

Color of 21 

Conductivity of 32 

Crystalline form of 22 

Divisions of 16 

Ductility of 23 

Elasticity of 27 

Expansibility of 31 

Forging 24 



Page 
Metal — Continued. 

Fusibility of 27 

Luster of 21 

Malleability of 22 

Noble 16 

Non-transparency of ... . 20 

Odor of 21 

Purity 25 

Sonorousness of 27 

Specific Gravity of 33 

Specific Heat of 30 

Taste of 21 

Tenacity of 25 

Volatility of 27-29 

Welding 24 

Mining. 

Gold Placer 249 

Gold Hydraulic 250 

Gold Quartz 251 

Mosaic Gold 161 

Molds 81 

Newton's Alloy 129 

Nurnberg Gold 192 

Occlusion 14 

Onion's Fusible Alloy 129 

Oreide 160 

Ores 

Alumina 185 

An Ore 12 

Argentiferous Galena . . . 213 

Brown Haematite 166 

Calamine 134 

Calaverite 248 

Cinnabar 198 

Copper Pyrites 153 

Galenite 98 

Greenokite 148 

Iridosmine 229 

Iron Pyrites 166 

Magnetic Iron 166 

Nagyagite 248 

Polyxene 238 

Red Haematite 166 

Silver, Glance 212 

Silver, Horn 211 

Silver, Reguline 211 

Spathic 166 

Specular Iron 166 

Stibnite 108 

Sylvanite 248 



348 



PRACTICAL DENTAL METALLURGY. 



Page 
ORES — Continued. 

Tinstone 114 

Oxides 

Acid Forming 39 

Basic 38 

Deoxidizing Agents 37 

Hydroxides 38 

Metallic 35 

Reduction of Metallic . . 39 

Zinc 140 

Oxidizing Agents 37 

Oxychloride Cements . . . 140 

Phosphate Cements 140 

Palladium 233 

Action of Acid on 235 

Alloys 235 

Compounds with Oxygen 235 

Dental Applications 234 

Electro-Deposition of . . . . 237 

Occurrence 233 

Properties 233 

Reduction 233 

Tests for, in Solution .... 236 

Palladium Bearing-metal . . 236 

Petroleum 58 

Pewter 104 

Phosphor-iridium 281 

Pinchbeck 161 

Platine au titre 245 

Pla/tinum 238 

Action of Acids on 244 

Alloys 244 

Compounds with Oxygen 243 

Dental Applications 242 

Electro-Deposition 245 

Fusing 240 

Occurrence 238 

Properties 241 

Reduction 239 

Tests for, in Solution .... 245 

Purple of Cassius 275 

Pyrometry 57 

Queen's Metal 112 

Red Lead 101 

Reduction 13 

by Electricity 48 

of Ores 60 

on Charcoal 73 

Red, Venetian 182 

Rees's Alloy 121 



Page 

Refractory Materials 50 

Regulus 13 

Roasting 14 

Rose's Alloy 129 

Rouge, Jeweler's 182 

Royal Mineral Succeda- 

neum 297 

Rules for Computing and 
Compounding Gold Al- 
loys 285 

Scorification 14 

Selenides 48 

Metallic 48 

Silvering , 295 

Silver Paste 297 

Silver 211 

Action of Acids on 220 

Alloys 221 

Amalgamation 212 

Blow-Pipe, Analysis 223 

Chemically Pure 217 

Compounds with Oxygen 220 

Cupellation 215 

Desilvering Lead 214 

Electro-Deposition of . . . 224 

Glance 212 

Horn 211 

Nitrate 218 

Occurrence 211 

Properties of 219 

Reduction 212 

Reguline 211 

Standard 222 

Tests for, in Solution .... 222 

Slag 13 

Solder 93-162 

Aluminum ; . . . . 194 

Brazier's 93-162 

Gold 280-284 

Jeweler's 280 

Silver 222 

Soft ...93-104 

Soldering 93 

Autogenous 94 

Spiegel-eisen 173 

Speculum-metal 122 

Speiss 13 

Standard Gold 278 

Standard Silver 222 

Stoves, Gas 68 



INDEX. 



349 



Page 

Steel 172-177 

Aluminum 176 

Alloys for Tempering . . . 181 

Bessemer Process 172 

Blazing off 181 

Blister 174 

Case-hardening 175 

Cast 174 

Cementation Process .... 173 

Chrome 175 

Copper 176 

Hardening 178 

Manganese 176 

Nickel 175 

Shear 174 

Spring 175 

Temper Colors 179 

Tempering 180 

Tungsten 176 

Sterling Silver 221 

Sublimation 14 

Sullivan's Amalgam 320 

Sulphides 41 

Metallic 41 

Reduction of 43 

Supports 78 

Tartar Emetic 110 

Tin 114 

Action of Acids on 118 

Alkalis on 119 

Alloys of 120 

Amalgams of 120 

Blow-Pipe Analysis of. . . 123 

Compounds with Oxygen 117 

Dental Applications 117 



Page 
Tin — Continued. 

Electro-Deposition of. . . . 124 

Occurrence 114 

Properties of 116 

Pure 115 

Reduction of 114 

Test for, in Solution . . . . 123 

Type Metal 112, 122 

Venetian Red 182 

Vermilion 205 

Properties 206 

Uses 207 

Wet Process 15, 154 

White Metal 161 

Wood's Metal 129, 151 

Zinc 134 

Action of Acids on. 142 

Action of Alkalis on 144 

Alloys of. 144 

Basic Cements of 140 

Blow-Pipe, Analysis 147 

Chloride of 143 

Counter-Dies 137 

Dental Applications 136 

Dies 136 

Electro-Deposition of . . . 147 

In the Arts 135 

Occurrence 134 

Oxide of 139 

Ox} T chloride of. 140 

Oxysulphate of. 142 

Phosphate of. 141 

Properties 135 

Reduction 134 

Tests for, in Solution .... 146 



4 



